Yea, I can see the problems that would arise now. And yes, while I agree the brothers should've been the ones to take her in, they weren't. I think I am sensitive to the idea of seeing a sick parent in the hospital simply becuz I've experienced that and it has left unpleasant memories. But anyway, you're right that taking the sister in would've opened the door for her father to manipulate OP and get his way so I can see why it would've been a bad idea now. And hah, I was actually comparing myself to the aunt becuz while she seemed to stick up for OP, she still sympathized for the half sister.

On a separate (somewhat irrelevant) note, I agree that there are many other children in need throughout the world, none of which are the OP's responsibility. And while blood relation tends to mean less and less nowadays, it is just my own belief that when you can help a child (or anybody, really), anywhere, in any way, you should. It's got nothing to do with obligation or whatever but just a sense of compassion I think people should feel for those who are helpless/don't know better.