Hi; I have life threatening nut allergies, and I have been sailing safely with HAL for the past 30 years!
I recommend eating, whenever possible, in the main dining room. Get to know your wait staff. They are always diligent. For instance, I was at afternoon tea when our waiter appeared at my side with a plate of delicacies special chosen for me! Another time, at lunch, he appeared with a basket of bread just for me.
At dinner I am presented with the following evening's menu. I fill it in, and sometimes, if an item is with nuts, I ask if it can be made specially for me - and it is.
HAL is wonderful. If possible, however, I recommend sailing with more than one epipen. That gives both me and my husband some security.
Have a wonderful cruise - your grandson will be in good hands!