It depends how much you want to 'make nice'. My gut instinct is that you probably don't WANT these people back. I also think you'd win in small claims court because you supplied what you said you would (it was for a 'donation' anyway) and they didn't like it. It wasn't inferior, it was simply not to their taste.

It's like someone ordering the 'special of the day' at a restaurant, then complaining that it contains garlic. They could have asked somebody before ordering, if they had known what the special was going to be before they got there, they could have looked up a recipe. They ordered it and took their chances, and they'll still have to pay.

It probably can be proven that these musicians don't make a secret of the political content of their shows.
You can probably testify that the women made reservations and donated money without asking about possible political content.
They bought a pig in a poke. If they do take it to court, I think you'll win and they're going to walk out looking a little less than bright. I also wouldn't think it would affect your reputation... not in any negative sense anyway.

If you want them to come back, you can refund the money and make nice. I can't see why you'd want them back.

Personally, I can deal with some politics, more if the political thrust agrees with mine. I walk out when I feel I'm being preached at, in ANY direction. If find myself not enjoying listening to musicians performing their typical act and I could have known about this beforehand, I would not later advertise my lack of clue by going to court for $20.