My kids are now 10 and 8 and for our next DL vacation this coming May/June, only NOW are DH & I considering doing 1 fancy sit down meal like at Carthay Circle. And even then, YDD won't appreciate much of the food at Carthay Circle (ODD is a more adventurous eater than YDD). My kids could handle a lunch at Carthay Circle but a 3 hour meal at Napa Rose? Forget it. We'll wait and do something like that when they are teenagers.
Also, something to be aware of regarding TS meals at fancy restaurants with toddlers & preschoolers - or, well, really any meal at a TS restaurant with kids that age - is that 1 of the adults present has to be prepared to pick up the kid and carry him out of the restaurant for a brief time out if/when the little one starts to flip out and have a temper tantrum. At CS restaurants, nobody really cares because all of those places are loud and it's kind of expected. But at a place like Carthay Circle or Napa Rose - those are fine dining establishments. If you & the other adults in your party want to eat there, that's great, but leave the younger kids out of it.
Children that age have really short attention spans. And a short amount of patience. When my kids were that young, I really had to time our eating out well so that we wouldn't arrive to the restaurant when 1 or both kids were at the "hangry" stage. And once said child announced, "Mama, I'm hungry!" I knew that I had a maximum of 15 min to get something in the kid's belly or else it would be epic temper tantrum time...which results in nobody having a good time.
Just remember back to when your kids were that age and use some of the tactics that worked well with your kids and it will probably work on your grandchildren, too!
It's not too much of a bummer that you might have to skip out on Carthay Circle or Napa Rose or Steakhouse 55. Look at it this way...it will mean that you have other stuff to try out on future trips with your grandchildren. With the age of your grandsons, they are that age where all of the characters at DL are the REAL deal. The REAL Goofy. The REAL Mickey Mouse. Children at that age totally live in the moment. Use this trip to look at it through their eyes and everything will fall into place and you'll have a lovely time!