This is a difficult situation! Both of your friends are thinking about what they want and not considering your feelings. You may want to sit down with each of them, privately, and explain that their arguing makes you uncomfortable. Tell them each that you want to continue being friends with them, but when they insist on one-on-one play, it puts you in an awkward position.
Three-way friendships can be challenging because one person tends to feel left out, even if no one is trying to exclude anyone. It may help to invite a fourth friend to join your group.
Best wishes in friendship,