I expect your brother probably has a lot on his plate at the moment. He's in the middle of a war, in a country where most of the population see him as an invader. This is hard. He has to build strong teams with his colleagues in order to cope with this. What little free time he has left, he is probably spending trying to build his new family. He's not rejecting you - he is just very much shorter on time than he was when there was just the two of you.
By all means write him a letter and send him gifts, but do it because you are thinking about him and hope he is well, not because you're testing him to see whether he sends something back.