Jackie, we can help your grandma a lot if she has questions, and we'll be very happy to answer the best way we can. Please show her how to make her own account here so she can come on by herself and ask the questions.
about snacks and food for meals: please read the stickies above for information about food. In general, food made with sugar and flour makes his blood sugar rise. This means bread, cake, cookies, pancakes, etc. Vegetables high in starch likes potatoes will do this, too. And white rice. So, in general, your grandparents need to know that staying away from that kind of food, or at least eating only very little of it, will help control his blood sugar. The best meals for him would be a piece of protein (like chicken, fish, or a piece of lean meat) and veggies and salads.
Snacks could be nuts, cheese, yogurt (not sweetened with sugar), celery with cream cheese or peanut butter.
His doctor should have given them some kind of information about diabetes and maybe suggested classes on nutrition. If the doctor hasn't done this, they need to ask him for more guidance for your grandpa's diabetes.
I hope this helps.