My friends are in a fight, what should i do?

Friend A is my cousin,(boy) and we hang out all the time, friend B is my neighbor and we hang out a lot too(girl). We all used to be friends, but this whole fight started but its really annoying, Im not quite sure how it started. They both always ask what the other person is saying about them behind their backs to me, but i lie and say they said nothing. Also if they see me texting they will ask who im texting and what we are talking about, and whenever i mention the others name the other will be like uggg. Also if either one asks if im doing something today and im hanging out with the other person, they will say eeeww. i tried once to get them back to gether, but it failed.....i dont know what to do please help.