what should i do/ my best friends don't get along anymore....?

well we used to all be close friends. we were like three peas in a pod and then all of a sudden things got complicated. girl 1 kept feeling " left out" like we never acknowledged her but girl 2 and i did.. she just never joined in the conversation. and if she talked it would be about her and only her.so we all just started hanging out separately so there would be no tension between us but then the issue came about that girl 1 had a huge crush on girl 2's older brother and two of his friends. the next time i hung out at girl 1's house she told me, behind girl 2's back,she came and told me that she was uncomfortable at her house ..BTW she stayed for the whole weekend and belles brother and his friends were only there for 20 mins. now girl 1 isn't allowed over because girl 2 thought that was really rude. now they are both friends with me, but don't like each other. girl 1 is upset cuz im closer with girl 2 and now i don't know what to do....