Surround yourself with friends and people that want to spend time with you. Seeing their posts on Facebook clearly upsets you so make it easier on yourself and block their posts from appearing on your news feed...you don't have to de-friend them, just block them and they won't know. You'll feel happier right there, I guarantee.
I've gone through a similiar situation with my brother and SIL, it hurts but the more I've involved myself with other people and friends, the less it bothers me. I hardly even vent about with my husband anymore, which is great because it doesn't change anything, just continues to bring up hurt feelings. You don't need them if they can't respect you!