I would send them home now with a warning to the parents about what happened yesterday and the fact that they were warned by you and presumably by the parents and that already they have forgotten how to behave properly and you are not going to take the risk that they will repeat today. The welfare of all children in your care is important and the baby deserves a place of peace and until they can behave they may not come back period. In effect you are giving notice without letting them officially go if that makes sense.

These two maybe should be in a daycare centre where they would be with peers and potentially in separate rooms to limit feeding off each other.

You need to make things ok for the baby to stay in care if you want to maintain your reputation. Family or not I would not be letting them take that away from you and right now they are.