Wishing you all the luck in helping him get on a regimen and stay there.
I watched my FIL die of diabetes related illnesses, and it is not pretty. He was cavalier about taking care of his diet and blood sugar.
He had a serious heart attack in 2007. Recovered from open heart surgery and gall bladder removal. Endured the death, and subsequent amputation of both his lower legs.
He continued to be careless about watching his blood sugar, and his diet. His next event was a lack of blood flow to his intestinal tract, and he died from it. It was very ugly.
I miss him every day, and wish I could have helped him more.