au!jason todd & bruce wayne | five degrees

The “brother“ in question is supposed to be Damian. Who is given to Jason to raise in “Batman: Death in the Family“ (which explores alternative timelines of what could happen to jason when/after he is kidnapped and tortured by the joker). In the film Jason agrees to raise him, planning to use the baby against Bruce as revenge and because he automatically hates the child for being just another replacement of him. But I think its inevitable he would bond with him, even unwillingly. And well everything else is just the standard Jason , wanting bruce to decide between him and joker, bruce being a flop, jason’s youth etc etc.