Who do I piss off?

Okay, small back story. My fiance works out of town, he's usually home on the weekends.

A family friend asked me and my kids to go with them to a movie this Friday. I agreed thinking my fiance wouldn't be home until later that night. But he told me they'd be coming home Thursday, after she had asked me. Her husband and my fiance work together, so I kind of have a feeling she knew they'd be home that day, but asked me anyway. I don't like being away when he's home because I don't get to see him often and we like to do things as a family. She knows this. She's an all or nothing type of friend. He wants to take our babies and go see a movie together on Friday. What do I do? Who do I piss off? I know it's a stupid question, but I'm a people pleaser. I hate having people mad at me, but something has to happen. Help?!