A.T.
Have you considered speaking to the children? They are at an age where they can hold a conversation with you. Try telling them you love having them play with your daughter, but if they can't follow the rules of your home (b/c they are at your home), then they will not be able to come over anymore. It seems pretty clear the mother will likely do nothing if you say anything to her. So, I would try that. Of course, since they have no discipline you will likely have to send them home a couple times til they get the idea.
You aren't disciplining the children, but you expect them to follow the same rules as you would your own children. As long as they are hanging out on your turf, that is COMPLETELY reasonable. It is cut and dry. If they can't do that, then they can go home and behave however they want.
I have a very similar thing going on with me, but the child is a family member, and thus unavoidable. However, he loves coming over to visit. You will have to take that away if the children cannot follow your rules. (P.S. Make sure your rules are posted or blatantly obvious.)