I think this is good advice.
Lynn, I totally get all the emotions you're feeling - the sadness, the anger, the frustration, etc. They are justified. But I think what you will probably see as time moves on is that you were all very fortunate that there wasn't a greater tragedy than loss of vacation time, and it's something to be thankful for that both of your grandsons are alive and recovering. Vacations can be redone.
We've had enough stuff go on in our family that we now have a saying. "As long as everyone's alive and healthy, we can get through anything." It helps us keep things in perspective.
I imagine the chef is probably feeling pretty awful about this. If you have it in your hearts to reach out to him to let him know the boys are doing ok now, it might mean a lot to him. It sounds like it was a mistake.
I hope your family gets some sort of satisfaction from Disney if that's what will help you feel better about the situation. It does only seem fair. But I also agree they will likely not be dealing with you, as grandparents; they'll deal with the parents. (Imagine if they had to deal with everyone's extended families every time something happens?)
Wishing you all well, and still want to hear what you thought of Melia sometime, aside from this happening.

Sending love and prayers to your grandchildren for their continued recovery.