Sorry to hear about your uncle.
I think you guys should do what you need to do for yourselves. It's something I have to argue with my extended family every Thanksgiving. Sometimes we just want to be by ourselves, or take a break from the routine (and that's without having a crisis happening at the same time). Everyone needs to understand that sometimes things happen and things change. It's called life! If you and your husband would feel better taking a family vacation to help process what's happening with his uncle, then you absolutely should! You have been very gracious in hosting it all these years, but shouldn't feel obligated.
And like you said, they don't really have to travel. It's not like people have sunk hundreds of dollars in plane tickets and hotels. They can figure out something else to do this year, and then next year you can pick up where you left off (if you so choose). Give yourself a break and put yourselves first this year. Maybe the rest of them can get together at somebody else's house so they're not alone.
Whatever you choose, I hope you enjoy yourself and find some peace in this difficult time.