Hopefully the OP is taking a honest third party look at himself and his parents and ensuring the situation is truly fair.
I think its great that the OP is out of debt and saving 50%.
Are his parents saving 50%?
Obviously, alot of other variables go into that, but the point is they may be sacrificing their own future while sonny hoards up a stash of cash. That would be pretty despicable on sonny's part.
Hopefully, that's not the case. If sonny is not a real drain on the household, its all good.
Perhaps nowadays, 'Failure to Launch' is looked down upon, but I also wonder if in decades past, multi-generational family homes had a better household contribution ethic than might exist today.