Hi. I think you have three main issues here, so I will try to suggest things for each in turn.

1. Growling when you pick him up - a lot of dogs don't like being picked up, especially if it interrupts something like play or sleep. And actually, I see that - I wouldn't like it either. Also, there is a reason for the saying ”let sleeping dogs lie”. That said, I totally understand why you are having to do it. As an alternative, can you try waking him by saying his name (if you can't wait until he wakes by himself) and luring him with something lovely like roast chicken or frankfurter sausage towards the stair, and only then picking him up to use the staircase?
2. The biting furniture, feet etc - this is just an extension of the boisterous play he had with his littermates but he needs to learn this is not how to play with humans. Some people find a sharp 'ouch' works but it can just ramp up the excitement. Some people find putting a toy in the dog's mouth works, others find the puppy is still more interested in nipping hands. My preferred method is to teach him that teeth on skin equals end of fun. So as soon as he makes contact, walk out of the room for a few moments. As long as the whole family is consistent - do it immediately and do it every time - he will learn. You could use a house line to draw him away, which keeps your hands both out of reach and also keeps hands for only good things.
3. Trying to take things away from him - always, always have something of higher value to exchange. The sure way to make a dog into a resource guarder is to just take things. The harder you try to take something he values, the harder he will try to keep it. And over time that will.just get worse and worse. So to teach him that giving something up is well worth his while, always swap for something better.

In your last paragraph you mention a few things that have been discredited by more modern research. Your dog won't think he is ”superior” - that is an idea based on a study of wolves and even the person who put it out there admitted he got it badly wrong. Dogs have lived in partnership with humans for millennia, but this one idea has become the flat-earth theory of dog psychology, people hook into it (largely due to certain tv personalities whose dog training ability is appalling). The wolf pack used was not a real pack, and the situation (captivity rather than wild) skewed the data as their behaviour was not natural. In a true pack, the leadership is fluid depending on the circumstances. And importantly too, dogs are not wolves anyway, the two species had a common ancestor as we did with apes; and clearly we are not chimpanzees.

This article explains it quite well. Debunking the "Alpha Dog" Theory - Whole Dog Journal

Nobody disagrees with boundaries and good manners, but the these can be established through training, building a mutually respectful relationship and without forcing submission from your dog. If you think about true leadership in your own life, the leaders (teachers , co-workers) that you respect earn that respect and inspire followership, they don't command or force it through wielding power 'just because they can'.

So please don't try to ”emulate” the mother's behaviour, your puppy will know you are not a dog. Growling at him won't make him think you are his mom, it will just make him think you are unpredictable, and that in turn is more likely to make him aggressive, because aggression in dogs almost always stems from fear - trying to scare off the frightening thing.

The best way to teach a dog anything is to ask for behaviour you want, and reward it. Pups struggle with ”no” because it is too general - even if they did recognise it as an interrupter for something they are doing, they don't know what that one thing they are doing is wrong (because they will be doing lots of things simultaneously like sniffing, listening, thinking, watching, playing and that one other thing, at any given time). And importantly it doesn't tell them what you want them to do instead. So, if your puppy is, say, jumping up - ask for an alternative and incompatible behaviour like a sit, and reward that.

You also mention being concerned over separation anxiety. Start by playing the flitting game, described about ⅔ of the way down this page -

Separation Anxiety - Fact vs Fiction

Separation anxiety is something of a hot topic, something many trainers and behaviourists avoid like the plague and something widely misunderstood by the majority! So what IS it, and what ISN’T it. Separation Anxiety is used as an umbrella term to cover any anxiety based issues regarding...

www.thecanineconsultants.co.uk

We also have some helpful resources on SA - Separation Anxiety

For general training I like the short videos on YouTube by Kikopup. You might want to look at ”Leave it” and ”Drop it” to support you in getting him to give up things he shouldn't have.

I've given you a lot to read here, hope it helps but please come back with any questions.

 

Thank you so much! This is all very helpful, and the articles you included were really informative. One remaining question I do have is whether or not the non-desirable behaviors such as intense resource guarding or biting (particularly biting associated with resource guarding) could return if, for instance, the thing that we are trying to take away is just too good to be substituted by anything else we try to "trade" and results in a child or relative getting bitten. Giving him a trade-up for a toy we're trying to take is good, as is giving him a toy to chew or bite instead of our hands, but is there a chance that his desires to bite and/or be more protective over his resources are just being harbored and could resurface later? And whenever we try to take something from him, should we always provide something else to trade-up, or is that only for training purposes? Just thinking of the small children in our extended family that he will be around in the future--I fear for a small child to be bitten if he/she takes something away from him but doesn't bring anything to trade-up. I'm also not sure if a "drop it" command will work if suddenly he is overcome by how much he really does not want to give something up?

 

I'd say that if he has something, the first thing you have to do is assess the risk. My dog is a scavenger and if we are out for a walk he has occasionally come across things he shouldn't have, like the remains of someone's takeaway meal. If it is undesirable, but not dangerous, I might not even try to get it (it get him away from it) because apparently there is little I can offer that beats a cold, 12 hour old curry or kebab and the worst that is likely to happen is explosive projectile diarrhoea However if it contains cooked bones, it is too risky, so I'd have to swap. If it was a toy he had, I wouldn't even think of taking it (I can't think of a reason why you would?).

Whether you would always swap really depends on how well he gets on with the ”leave” and ”drop” cues. Dogs seem to get more engaged with any training cue (once it is solid) if you switch up the rewards - sometimes high value, sometimes normal food, sometimes an ear rub. Apparently it's similar to why people play slot machines. So maybe your reward becomes a ”good boy” sometimes.

This is a great video about ”drop it”

In general, I'd recommend always having baby gates to keep him and children apart when you are not actually there, and teach children not to approach him if he is sleeping, eating or engaged in anything like chewing something.

I'm also going to tag @JudyN who has experience of resource guarding, and may have more to add.

But - I don't think it is inevitable that he definitely will be a resource guarder. If you do the leave, drop and swapping things now, it's possible it may not happen at all.

 

Excellent advice from @JoanneF

Your dog sounds rather like mine, even though mine grew up with his mum siblings till 7 weeks, so I'm not sure where his issues came from. So a few things I'd say in addition:

If he carries on being growly about being picked up, you could try feeding him bits of chicken or something while you're carrying him, so he thinks being carried is awesome. If this doesn't work, though, I'd suggest that the risk to his joints from walking up and downstairs a few times a day is less than the risk of him becoming increasingly growly about being picked up and biting as a result, maybe if someone just approached him if he thought they might be about to pick him up. Just take him up and down on lead so he can't jump the last 6 steps at once.

I'm wary of the trading approach, because in my dog's mind, if the plastic spoon he's chewing is so valuable I'd actually offer him a lamb steak in exchange, the spoon must be REALLY valuable and he's going to REALLY have to fight me for it (yes, this happened!). So my approach is, if he has something he shouldn't have... it's his. Even if it's something harmful, because trying to get it off him (a) will potentially be harmful to me, and (b) will reinforce that I'm likely to take something desirable off him, and potentially make him guardy if you just walk past him when he has something. This obviously means that you don't leave things lying around that you don't want him to chew/eat, and you let him decide when he's had enough of any long-lasting chew. I don't give my dog long-lasting chews, bones, etc. because the risk is too high. In the early days, he'd bring a chew over to us, sit chewing it at our feet, then growl at us because we were too close

Alternative strategies are to teach a really good recall within the house, so when he has something you can call him from the other end of the house (opening and closing the fridge door if it helps) and, hopefully, he'll be so keen to come that he forgets about what he has. You don't want him to think that you are after what he has (some dogs have very suspicious minds) - give him a huge reward for coming, and work on this in a situation where you can then let him go back to what he had so he doesn't learn that recall means he'll lose something.

Another useful command is 'Bring it to me' - i.e. instead of simply dropping something and you getting it, he actually does bring it over to you in exchange for a treat. The positive of this approach is that if he brings it, you know he's OK about you taking it, and if he doesn't, you know that going and taking it, or even going up and petting him while he has it, may not be such a great idea.

The more he can feel comfortable and secure now, and not anxious that he might be challenged to give up his new best possession, the less likely guarding is to become a problem, and the less valuable his new possession might seem.

One caveat - my dog isn't at all chewy, and non-food items soon lost their high value. Whereas he used to get very guardy if he had a sock he'd nicked from the laundry pile, he'll now bring me socks, pants, hankies etc. he finds lying around, and he still gets a treat. But if you have a chewy dog (which a lab cross may well be, 'chew toys' like shoes may always be more appealing, so might continue to be high value for longer. Just be very aware of what's going on in your dog's brain - if he thinks trading is the best game ever, then all well and good, if you think there's a little reluctance, maybe go more with my aproach.

 

Thank you both very much! Very helpful info that I'll be sharing with my husband!