I can understand how you feel about your husband.
One of my close friends has a male friend who is a tall man with a big build who I will call John. My friend was overweight as well and a few years ago she said to John we both need to lose some weight because otherwise we will end up with health issues like diabetes.
John attitude was so what if I get diabetes.
My friend lost weight and John continued to put on weight.
John now has type 2 diabetes, sleep apnoea and high blood pressure. He has been in hospital a few times due to his blood pressure going extremely high. His diabetes meds are being changed a lot as well to control it.
My friend lost a few stone back then with slimming world. She could eat plenty of good food.
She had syns each day so she use a few for a bit of chocolate. She started to cook more food from scratch, eat more fruit and vegetables. I know that slimming world have men only classes as well.
At this stage you need to sit down with your husband when the kids are not their and tell him that your worried about his weight. Tell him that you had enough of him refusing to do anything about and this is his last chance with you. He either does something about his weight or it over because you can't bring up your children and mind him after he has a stroke or heart attack. Tell him that the kids need both of you well to bring them up.
I would tell him about slimming world, show him the website and get him to join them. Get him to do body magic as it will help get his fitness back and help him lose weight.
You need to bring him to his doctor for a health check and go in with him. He may have sleep apnoea ect. Perhaps been told by a doctor that he needs to lose weight for health issues might help him as well.
I know it won't be an easy conversation to have with him but you had enough of watching him getting heavier and he is not physically able to do much with the kids. The reality is that you have kids and you both need to stay as well as possible to bring them up. You don't know what could happen either of you in the future and the other person needs to be fit enough to mind the kids if the other person is not well. I know several men who were left to bring up kids after their wives died as well so that why you both need to look after your health.