I so miss my Grandma, even though she died when I was 6. I still remember sitting on her lap and playing with a necklace she wore, and the smell of her homemade tortillas coming from the kitchen. My dad is now dying, and both he and Mom have dementia. I research our family's genealogy and asked my dad a question about his uncle a few days ago and he started crying, twice. I felt terrible, I'd forgotten that old memories are freshest in his mind, and the sudden, unexpected, violent death of his uncle seemed to him as if it happened last week. Also, I'm a Grandma myself, with grandchildren from SoCal where I live, to New York to Germany. So this is all where I'm coming from...
Your annual visit is done, so this conflict won't come up again until next year, right? Of course if it's all too "horrible" (and I don't say this in sarcasm or criticism, Lisa, I'm merely quoting what you wrote) for you to deal with they could stay at a hotel. But my suggestion is that you and your husband sit down and talk it over before the next visit. Be somewhat flexible with the dinner time, say move it to 6:30 to accommodate everyone, and call Grandma before they arrive to let her know this, and that everyone will be eating dinner at that time together. Bath time can take place before dinner, say from 6-6:30, then afterward dinner, a story or two, brushing teeth, potty and bed, which should still be able to be accomplished by 7:30. Your kids will be a year older by then, too, and could surely benefit from spending time with their grandparents over dinner. And even if they don't nap anymore a "quiet time" where they lay in bed with just books for 45 minutes to an hour is always beneficial.
It is your house, and, yes, you can lay down the law, "Dinner is at 5:00," but if it's once a year my advice is to work together, tell Grandma you can move dinner an hour later. There's no reason you need to cook separately for the kids and clean up a separate mess, just offer a helping hand to Grandma in preparing dinner, (she'll probably refuse as she likes to do it herself0 and if Grandma cooks the meal you, your husband, and Grandpa can clean up as a "thank you" to her for cooking.
Family and pleasant memories are way more important to me than schedules or resentment, kids are SO much more adaptable and flexible then we give them credit for, and nowhere have I seen that anyone is guaranteed to be alive even tomorrow, let alone a year from now. Spend your time and energy enjoying their visit and encouraging a relationship between your children and their grandparents ~ blessed are the flexible✿