I have never had a good relationship with my sil even from beginning of brothers and her relationship. From what I understand my sil had a difficult childhood which may explain her behaviour. Things didn't start well because at our first proper meeting at a family event she was quite rude and things didn't get better from there. I had very little to do with her until she fell pregnant with my first niece after that I tried to get a long with her but then she would post things on facebook which offended me and at times I feel she is very controlling towards my brother. Fast forward to today with me and my dp planning our own family I want a relationship with her as my kids and hers will be cousins but I worry that there is too much water under the bridge to start a relationship which is good for every one involved especially the children.