I think my biggest fear is mom will want a late start in the afternoon and then call it quits early evening after dinner. That leaves a very small window for the parks and it's the peak hours of the day for most people; so, it will be the most crowded. I think her happiness will come from watching TV or being on her phone more than being in the parks. She's not sickly, but she's very passive about everything. I don't have a passive bone in my body. Hence, this is the conflict I'm facing with this Disney trip.
I've read over this thread, and to me it really sounds like you want to take your grandkids to Disney, but not their mom.
And that's fine! I have family members I won't take to Disney, either, because it would put too much stress on our relationship. I also have family members who believe that if they're paying the bills, they get to call all the shots. Fortunately, I'm experienced enough now to be able to politely decline gifts like these. It would be much harder to say no, though, if it was presented as a gift for my kids.
I also recognize that your husband isn't in great health, and you're worried that he might miss out on the opportunity to see Disney with the kids.
But, if at all possible, I still think you might be better to wait a few years and take the children alone, when they're old enough to travel without their mother. That way you can set whatever schedule you like.
If that's not possible, then you're just going to have to adjust your expectations. This is your grandchildren's mother! And she's on vacation, too. So, forget about how much you need to accomplish to justify the price of the tickets. Once it's paid, that money is gone. Focus instead of working WITH her and ensuring that
everyone has a pleasant vacation, without family conflict. If she and the kids decide they want to sleep in - let them! Go spend a few hours in the parks with your husband and meet up with the family later. Discuss the options with your grandchildren's parents openly and without judgement or criticism. Respect their wishes.
If you go ahead with this trip, it will be a very different trip than the kind you're used to having. Embrace that idea, and you'll be much happier.
Remember, a gift shouldn't come with strings attached, especially emotional ones. And trying to dictate someone else's vacation plans is always a recipe for disaster.