[WhisperingSilence]

Hey, I've been in a similar situation, when two of my friends fell out, they didn't want to be around each other and they would both get upset if I spent time with the other one, eventually I spoke with a adult I trusted (in this case it was a staff member at my supported living home) and they helped me, we decided I needed to like basically tell both of them that I want to be friends with both of them and it doesn't mean that I am going to ignore one or the other, and that I will still be friends with both of them. I then explained to both of them that I do not want to be put in the middle and be made to pick sides and listen to them slag each other off behind their backs as it puts me in an awkward if not incredibly difficult situation, sadly the friendship with the other girl who I was not as close with fizzled out as she kinda like began to shut everyone out..
I think you need to sit down and talk to them both individually and explain you wish to be friends with both of them and explain that you are not going to leave one for the other and just ask them to trust you and explain to them that you will hang out with them separately and its not that you are picking sides or choosing one over the other.

if they are real and true friends they will respect this and your decision.