Based on what you have said here, I would call my mum and say "I really need you to support me at this exhibition. Brother has heaps of people with him." At the end of the day, I really wouldn't worry all that much about what he phoned me to say. Yes, these things are upsetting, but that's the way it goes. You can't please all the people, all the time! Families are difficult. We are never going to get on with everyone just because we were born into the same family!

And, yes, I think your brother is being phenomenally childish.

If I lived closer, I would be there!