My cat, Elfie, went through an aggressive stage around the age of 3. At that time, I was about 10 or so years old, and my sisters were 9, 6, and 3. He has always been a strong willed, proud, and independent cat. I think he got to a point where he was like "you know what? I'm tough, young, and strong and so TOTALLY awesome, I don't have to take this crap!" Sick of all the harassment he got from living with so many little kids, he began attacking, biting, and being totally rude to everyone but my mom. Granted, he never drew blood or actually REALLY hurt us badly, it still hurt and startled us when he would attack!
The solution? My mom worked very hard to make sure that us kids gave him space. We got kitten Rusty, so us girls could have a kitty to love and let Elfie get over himself. He got affection on his terms- when he sought it out. Ten years later and he's just a perfect gentleman. He hasn't bitten or swatted anyone for years now, and he's very mellow and laid back.
I would have a talk with your family. Tell them, yes, Oswald has a little issue but that it can be managed as long as everyone ignores him. When he comes seeking attention, give him a few pats. Leave him wanting more!
Never let it get the point where he gets sick of the petting. While most cats would get up and walk away, some cats feel that it is necessary to lash out or bite to let their owners know they have had enough. Watch for his early warning signs: tense posture that may be accompanied by stiffening of his muscles (especially in his back/haunches) dilated pupils, sudden stop of purring, a change in ear orientation, staring intently instead of relaxing with narrowed/closed eyes, and a big one to watch for is the thumping, lashing, or maybe even twitching tail. These are all warning signs that kitty is getting annoyed. Some cats are very subtle about their warnings and will lash out without you having noticed the signs. You must be watchful, and remember that the less attention you force on him, the more he'll come searching for your attention later!
Another thing you can try is hand feeding him part of his meal, kibble by kibble. This is a good way to strengthen the bond between you and your cat. Get his bowl of kibble and walk around the house, encouraging him to follow. Give him a kibble every few steps. (This is also a good way to teach your cat to come to you when called!) The idea is that Oswald will see your hand as something really good. When you reach down to him, he gets a tasty reward, and he'll come to like your hand.
Another thing I do with my cats when they bite me is I'll go "Ooooowwwwweeee!" And then I'll pout and walk away from them. I might even toss a hurt, devastated look towards them over my shoulder before I leave the room and proceed to ignore them for a while. It doesn't work with all cats, but at least with my kitty Nito, he can't stand it and he'll come find me, jump up next to me, and act all cute
I know it can be hard, but be patient with Oswald! A lot of cats can go through a "terrible teens" phase, sometimes even during their adulthood and not their adolescence. Most cats calm down with age and patience.