I would tend to agree with a lot of what has been said here; seems to me like you have a case of anxiety and insecurity.
The muzzle is a good tool to transition as it will help you feel more comfortable and confident, knowing that Oscar cannot bite even if he wants to. If you couple the muzzle with counter-conditioning, you could likely get to a place of eliminating the biting.
For my dog, the point of issue has been the doorbell (a very common problem-area, I think), she loses it
when the doorbell rings. I began by playing a recording of our doorbell very quietly from my cellphone and giving her tons of roast beef (high value treat, my dog happens to have a poultry allergy) when she perked her ears up but stayed completely calm. I have gradually made the sound louder and did it at unpredictable times of day, maybe 20x per day, until now I can play the bell at full volume without her reacting. Now we're working on knocking
Similarly, if you muzzle Oscar and take him around strangers where they won't interact with him; you could employ the people he's taken a disliking to to stand around and ignore him while you walk him and feed him treats when he notices them, but doesn't react aggressively. This could serve both to build Oscar's happy association with the people you want him to like as well as help those people learn to trust Oscar again, all in one fell swoop. I find food and beer can help coerce audience participation, of the human variety, of course.
As Oscar relaxes around strangers who are completely ignoring him, you can gradually move to a closer proximity, treating so long as he is ignoring them too, until you can eventually have his least favorite people give him a pat or even just look at him. He's got to learn to trust that you won't put him in the presence of someone who would hurt him.