Can a beis din rule in monetary matters that concern them? For instance can they rule that Simon owes Levi and themselves? Or must it be brought to a unbiased beis din?
Shulchan Arukh CM 7:12
כל דבר שיש לדיין בו צד הנאה אינו יכול לדון עליו
Any matter that the judge has some benefit from, he is not allowed to judge it.