The best advice I have for anyone working with diabetics is to keep an eye on their blood sugar levels. Your clients should have tested their blood sugar prior to exercising to determine if they are safe to exercise or if they need something to raise or lower their blood sugar prior to exercise.
Keep in mind that cardio generally lowers blood sugar levels, while strength training generally raises blood sugar levels.
A resource that I found is a book called, “The Diabetic Athlete” by Sheri Colberg, PhD. She covers a variety of sports and advice on blood sugar, medication, and nutrition for over 86 different sporting activities. Good read!