She sounds like she is losing it OP. I would go with the kids but stay away from your parents. Then go see your mom and dad after your kids leave and give your dad a break. Sounds like you really need to talk to him about hiring help for Mom's care.

You really need to call them out on their staggering selfishness.

Go for spring break. Flights to Europe are hideously expensive this summer due to major sporting events. Don’t tell her.

Your parents have become extremely selfish in their old age and anxiety due to medical complications.

Visit all your other relatives, enjoy your country! You need to emotionally detach from these two people. You cannot save them from their codependent mental prison.

What country is this grandma from?

Why does she get to have your help and devotion as she treats your kids like pesky nuisances to be kept away, and she doesn't care about you much either? I would not go out of my way for this woman at all: as in I'm going to Hawaii with the kids, and she can recover alone.