I don't know if I can give you any advice, but I don't speak to my brother and SIL but their son and my son share a b'day. I've decided to invite only my nephew to our DS's party, but will extent the invite to my brother as well since it was mostly my SIL that I fell out with. I simply don't want her to come to my DS's b'day and spoil our day. If we get an invite to our nephew's b'day party, we've decided my DF will go with our DS.