I would just suck it up yes. The same way I have sucked up Disney three times, have sucked up spending all fucking day once a week in the summer hols at a localish park I hate and every year I suck up spending every day on the beach rather than visiting the historic castles and museums that I love and paying for the privilege!
When kids are very small you have to really adapt on hols. But once they hit 8 or 9 you can have a bit of what you want too. Plus you can actually not go to disney if you don't want to. It isn't a graduation requirement for childhood.
I am very happy for those families who love disney (our best friends go all the time plus cruises, the parents love it and they are always asking us to go with them - we say no), but I really hate the idea that a trip to disney is the sine qua non of a childhood holiday. No it isn't. Like I said upthread, my children have had lovely holidays every year in Florida in very beautiful surroundings with family and have never been to Disney. I've had no complaints. They have loads of lovely memories.
The relative who funded this holiday probably got a lot of oomph out of the "and you are all going to DISNEY" but in reality a trip to Mallorca or Greece in a villa for a week could have been just as lovely for everyone and formed really great memories. Nothing wrong with disney but is isn't a requirement and a lot of adults hate the concept - especially if it happens after a long haul flight and in 90 degree weather with humidity.
Our absolute best holidays ever were in the UK and also in Scotland visiting historic castles and museums - and battle sites (I will say we don't live in the UK so it was "exotic" to our pre-teen children). They loved them. Those 2 holidays are among the best we've had. And my children are very normal, not particularly into history or learning anything on hols.
Given the way this had gone, I think the husband has to go, be cheerful, and help out and then say thanks so much for a wonderful time for our family. But he doesn't have to pretend to his wife that this is the best thing ever to happen his holiday plans- it isn't. And he is perfectly entitled to want some time away from the extended family/theme parks - maybe with his wife and children.