How do I tell my mom I cannot watch the dogs?

Me and my fiancé just moved about 3 hours away. We’re home for the weekend to grab more stuff and see family.

My mom asked me if I could watch the dogs at her house while she attends my cousins wedding.

The current plan for tomorrow(could change) was go see my fiancé’s sister and her family then he’d drive back to where we currently live and I’d stay here for the week because I have family stuff going on. He’d then come back next weekend and we’d drive back together.

I figured my fiancé’s mom could drop me at my moms(I don’t have a car with me) and I could watch the dogs.

I asked my fiancé the plan for tomorrow citing that my mom asked me to watch the dogs due to my cousins wedding. He had no idea and then asked why my brother couldn’t do it(he hates staying alone so he’s staying at my aunts, I told my fiancé he was away) then started talking about the wedding and thought it was odd we were not invited(it’s a small wedding).

What do I do? It’s becoming way too complicated. My mom treats the dogs like her babies so to speak and wouldn’t ever board them, doesn’t like leaving them alone at night and feels like it’s a bother for someone to drop in to let them out/feed them because they get fed human food(beef and rice).