How long have you tried all the things that you have tried? Because consistency is key.
First of all, I would try to modify the stairs. Even if it is just a non slip towel you put over the stairs when you go out, and then take with you so your neighbours will not be bothered. Is the concrete sanded or rough? It can be they simply find it too slippery, and therefore do not want to walk on it. In that case, perhaps ask your neighbours if it is okay you put anti-slip strips on it?
I think positive reinforcement can be the way to go. First, feed them treats or even their daily allowance of food from the first stair. Do not push this to the second one, they have had some experiences now already. The stairs are not neutral for them anymore, they are negative and scary. So just feed them on the first stair, do not make them climb it afterwards. Do this for a few days, or until you see they have no sign of discomfort at all to being near the stairs and eating on them.
Then see if you can put it on the second stair, continue.
Eventually, try to put the food in such a way that they have to actually step on the stairs. If they put all 4 paws on the stairs, click and give them the food (or lots of treats). Whenever you have a success, don't force it. Continue the same level of difficulty in a few more sessions (do not make sessions too long, you will build pressure in the dog) until you see the dogs being comfortable again.
That is what I would do anyway! Hope you figure this out.