Wow jaw dropping self centered-ness. My grandparents' places were also some of my favorite places growing up, but the idea of asking a cousin to go without his disability aid once a week so that I could experience that twice a year just blows my mind. For competing needs, seizure alerts trump animal allergies by a lot in my mind. Also I love the direct assumption that their kids will feel second rate, like that isn't something parents can directly address and model graciousness on.

Maybe they should think about asking Grandma and Grandpa to come see them four times a year (and offer to pay or at least help with the extra travel expense if they can), or find something local to Grandma and Grandpa's house they can maybe do as an annual daytrip? I get that spending the whole time in a hotel is a bummer, and it sounds like their allergies are severe enough they won't be able to set foot in the house at all. They are going to have to find some new ways to keep that relationship flourishing, but that's not such a great hardship under the circumstances.