I am super sorry that you didn't get anyone responding yet!! Genetics can be a pain in the butt when they work against you. I have this with familial hypertension and cholesterol. My blood pressure wants to go high, my HDL is hard to make rise even when active. My thoughts. Your husband is doing all he can and SHOULD keep doing it. It's only going ot help and has other benefits. But once there is a sign that we are losing the battle of treating things the natural way (he is of proper weight, eats healthy, exercises, gets plenty of liquid and rest?) . . . they make medications that are GREAT. Do not be afraid. I put off my blood pressure medication for a long long time. Finally my doctor said that I was putting so much pressure on myself and living with anxiety that I just couldn't do enough to keep on it, how about I just started a low dose of medication. One of THE best health decisions of my life. And part of life is that you can't give up everything you like. If he won't give up the flour, okay. Talk to his doctor. Maybe he can cut back. Or you ca sneak some substitutes in. But going ahead and treating this medically could get the diabetes under control and the worry of complications from it put to rest.
My blood sugar and cholesterol rose after exposure to toxic mould. Inflammation grrr. Diet wise, try raw honey.
“It seems counterintuitive that honey actually lowers blood sugar levels. But the science clearly shows that it does. And furthermore, it appears to lower cholesterol as well. This supports what I often see with clients and customers. While the study didn't state how much honey was administered each day, we see amounts of 2 tablespoons per day working effectively.” - Excerpt from Bee Buzz - Raw Honey and Diabetes.
Diabetes is not just about sugar. BG rises from all carbohydrates which includes bread, rice, potatoes, pasta, fruit, and of course more. However not all carbohydrates increase BG as quickly as others. I would suggest you google "glycemic index". It is a measure of how fast the impact is from carbohydrates. There are on line lists of foods with their glycemic index.
There is only so much you can do with diet however. Some doctors are willing to prescribe metformin for prediabetes. You may want to ask about it. It is a safe and very inexpensive drug that has been used for the initial treatment of diabetes for decades.