His weekend is his weekend. If there is some issue with it, he will need to figure out how to get Marc where he needs to be. Time to man up and be a Dad.
As for what you let him know about your plans, they are unbreakable and since it isn't your weekend, it isn't really an issue.
kat
Me-53(and learning!) S24, S21, D18, D17 Just keep swimming, Just keep swimming. Dory