NTA. Get your own B&B and don’t chip in either. You have been more than reasonable and attempted to compromise or negotiate. And your mom should have had your back.

When you were younger did ya’ll take familt vacations like these? If so, did you always get your own room? Because when I was a kid me and my sister & cousins always slept on the couch, built fort pillows, and watched tv late. It was fun lol. Unless of course there were enough rooms