I saw the hotel suggestion...so here's what i would do. I would wait to see if the other couple decided to get a hotel, first, and if they did, then cottage is all yours. If they decide to show up, then I go get a hotel room.
Not a fan of weddings. It's the neighbor's kid? That wouldn't be something I would be too worried about not attending.
What I would probably do now that I've reread your original post is ... forget all the 3 day nonsense and drive in for the actual wedding then bolt back home. 3 hour drive is diddly. No way it's an AM wedding so you have plenty of time to arrive. If it's an evening wedding you're getting home around midnight or so. That's what I would do and problem solved. Asking you to attend a 3 day event is a little much.