OP my point about the name calling is that it’s not an effective way for your girls to deal Ben (or anyone else who name calls).
Much better to say “that was a very unkind thing you said Ben, it hurt our feelings. We won’t want to play with you if you are rude and unkind”.
Escalating name calling just means (by the time they go to school) that everyone gets into trouble, rather than just the person who started it.
In your situation it doesn’t let Ben know he’s done anything wrong or hurtful. It also means Ben’s Mum can brush off his original bad behaviour by saying “well your girls name called too”.
Clearly you think I’m being harsh. It’s honestly not my intention.
It is my intention to point out the consequences of putting social politeness to your friend over dealing with her child’s behaviour.
Ben’s behaviour goes unchecked because his Mum is either struggling or ineffectual and your girls see that he behaves as he likes with little sanction. They respond in kind to defend themselves and the whole thing descends into disaster, an uncomfortable situation for you and an upsetting situation for your girls.
You are left seething every week and they are left confused and end up retaliating with the exact bad behaviour you dislike in Ben.
Ben’s Mum isn’t going to do anything about this, so you have to for the benefit of your girls.
Unfortunately that means you are going to have to behave in a way that’s uncomfortable for you by putting boundaries and consequences in place for both Ben and his Mum.
Better to step outside your comfort zone than to abandon your friend though.
This stuff isn’t easy. And no one warns you that it’s part and parcel
of parenting. It doesn’t go away as they get older either I’m afraid.
Best of luck.