Hi and welcome.
Sorry to hear about the health issues your husband is facing but I like your use of the phrase " That WE need to make some lifestyle changes" as it will help him if you are also embracing the changes and likely do you good too. Are there any activities that you used to enjoy that perhaps have fallen by the wayside that you could take up again together.... dancing or walking or cycling or playing table tennis or gardening or swimming?.... It doesn't have to be overly exertive, just something to get your bodies moving a bit more and the blood flowing and the lungs working a bit harder. If it is something you both enjoy that will obviously encourage you to stick at it on the days when you/he are less motivated.
As regards dietary changes, there are two main approaches but some people are successful with mixing and matching...
The very low calorie Newcastle/Fast 800 diet is usually a meal replacement shakes based diet of 800 calories a day and is designed to make your body burn off the visceral fat around your liver and pancreas. It is a short term 8-12 weeks program where you are looking to lose about 15kg. If your husband is started on medication for diabetes then this may not be an appropriate course of action, so it is important to discuss with your GP or nurse. This program is promoted by the NHS in some areas so it might be possible to do the diet on the NHS but it can be self funded using any meal replacement shakes. Exante was one of the original manufactures used in the research program I believe but many people use supermarket own meal replacement shakes like Tesco's own brand. The key issue with this option is that you maintain the weight loss after the diet is over. Some people find that the period of shakes help them to reset their relationship to food, but some people find that reintroducing food means that they slide back into their old ways.
The other main option is to reduce the amount of carbs he is consuming. This is more a change of way of eating for life rather than a quick fix weight loss diet. It takes a bit of getting your head around at first but it can be quite enjoyable once you learn to experiment with different ways of using foods. For instance, bread, pasta, rice, potatoes and breakfast cereals are all high carb foods so you start by reducing your portion sizes of those and having more of the lower carb stuff. So one slice of bread instead of 2, but more meat/fish and salad in that one slice sandwich, or 3 scrambled eggs on your toast and add in some mushrooms and a tomato. I like omelettes because they don't need bread as a carrier or to soak up a soft yolk and I can vary the fillings and have it with a big plate of salad and a big dollop of coleslaw (usually cheese coleslaw because it is tastier)
Cauliflower can be boiled, drained well and mashed with a dollop of cream cheese and a spoon of mustard to replace mashed potato and used either like that or as a topping for cottage/shepherds/fish pie with a good sprinkle of cheese on the top. Cauliflower can also be grated and stir fried to replace rice with a curry or chilli or Chinese dish.
Celeriac or swede can be used to make chips.
I tend to have bolognaise sauce on a bed of courgette or broccoli or shredded cabbage, usually cooked with a knob of butter. You can get Konjac rice or noodles which are largely fibre and pretty well zero carb .... "Bare Naked" is one of the most well known brands. You do need to rinse them really well before you cook them as they come in a preservative liquid and usually a quick zap in the microwave for a minute is enough, so very convenient. Other people use egamame bean pasta which is lower carb than wheat pasta.
Don't be fooled into believing that changing to wholemeal bread, pasta, brown rice alone will work. There are almost the same amount of carbs in them than the white version. Yes, the extra bit of fibre is good but you can get fibre from much lower carb sources and ultimately, it is the carbs which count because they all break down into glucose in your digestive system and release into the blood stream, where as diabetics, out body has difficulty dealing with it.
Not saying don't eat any of these foods, but reduce portion sizes of these high carb foods and learn to use lower carb substitutes. There are low carb breads you can buy or make if you are a keen baker and in fact lower carb cakes and biscuits although I am not a fan of artificial sweeteners so I just really limit my intake of sweet stuff (I was a sugar addict pre-diagnosis, so limiting sweet stuff keeps me on the straight and narrow) and I now have a much greater appreciation for savoury and sourness and even bitterness as different taste experiences. It is almost like I now eat in 3 dimension whereas before I was just eating in 2 dimension or eating in colour now instead of black and white and I find sweetness in things I previously thought were sour.
Anyway, eating this way has had massive health benefits for me not just with my diabetes, so it has been well worth changing and I still enjoy my food, I just eat different things now and I certainly still have plenty of food treats, they are just not the sweet ones I used to indulge in.... far too often. I am also rarely hungry because I eat more fat and that fat gives me slow release energy rather than the carbs which were giving me a massive spike and then lull. Often I am happy with just one or two meals a day. Having 3 is unusual these days and I just don't miss those meals, particularly if I am busy and getting plenty of exercise. Interestingly, the more exercise I get, the less I need/want to eat.
Anyway, just wanted to outline the two main approaches and give you a little insight. There is lots to learn and 4.5 years down the line I am still learning and making mistakes, but mostly getting it right.