Many of us were raised where 'no' is something you only say to strangers selling things. To family? You say 'let me see', then you show up, tired, carrying a tray of food.
Practise this: 'I can't this weekend, but I love you.' That's it. No essay. No list of reasons. Over-explaining invites negotiation, and some of our relatives negotiate like they're at the market.
Said no. Did you die? No. Exactly.