Happy 30th in advance!!

I personally wouldn't be worried about it being Mothers' Day, but I'm always surprised by some people who make a really big thing of it and get their noses out of joint about stuff being on that day. Ultimately, though, if it's a huge problem people don't have to come!

Could you maybe make it breakfast/brunch/afternoon tea (a really nice one)/dinner? That way the precious 'lunch' spot is free for people. Or, could your family come on the Saturday night?

Just do what you want to do, but don't be disappointed if some people elect for a more traditional Mothers' Day.

HTH