I agree with Eloise. I still think BIL is a dick. And I probably would have been yelling in the background, also. I think H should grow a pair. However, this case illustrates why I always set expectations explicitly for holidays. If you don't let your expectations be know, you cannot be disappointed when they aren't met.
I feel like it's pretty damn reasonable to expect your H to know that you'd like to spend your first Mother's Day with your kid AND him, whether you've stated it explicitly or not. Maybe that's just me.