Fellow fat person here (albeit, only a small-mid fat). First, I want to preface my comment by reminding you that none of us here are your partner's physician, so we can't provide any medical advice. I won't give advice about the yard work or the sex, since the underlying issue seems to be with your husband's size, rather than whether he can use a lawnmower. What I am going to say will probably get me crucified by other commenters, but it'll probably be the only sustainable advice you're going to find if you want your relationship with your husband to last.

Don't pressure him to lose weight. Don't get his family to pressure him to lose weight. Weight loss for the sake of weight loss will only cause your husband to gain more weight. Diets have an almost 100% failure rate. The weight loss industry knows diets don't work and that is why it is a multi-billion dollar industry, so it's important to stop placing blame on your husband. Pushing yet another diet on your husband is not going to work in the long run, especially when other social determinants of health aren't being addressed. In fact, yo-yo dieting is actually more of a risk factor for inflammation which causes a lot of the chronic health conditions typically associated with obesity. Health is so much more complex than the fat we carry. And I am telling you from my own personal experience, lecturing him that he's slowly killing himself is going to ruin his mental health, which is just as important as physical health.

I'm paraphrasing work by Linda Bacon and Lucy Aphramor here, but basically our bodies are designed to be as efficient as possible when it it comes to using energy, and putting your body through periods of what it thinks is famine ends up exacerbating this mechanism we gained to survive periods of food insecurity. This is also why people who diet become preoccupied with food and then binge when the diet inevitably fails- your body is basically screaming "EAT RIGHT THE FUCK NOW, BITCH!!!!" using every way it knows how to make sure you get the energy you need and then some in case it happens again. This is also why even people as fat as your husband could eat the exact same diet as Jillian Michaels and still not lose weight. I'd also mention that chronic stress can also contribute to weight gain. Food literally tastes better to you because your body is freaking out and thinking it might need to suddenly use a lot of energy. It would rather get that from food than from its fat stores because like I said earlier, humans have evolved to put on fat as easily as possible. Being a fat person in a world that would rather you die or not exist at all is a chronic stress and traumatic as fuck even for me, someone who is a little over half your husband's weight. I can't imagine how traumatic it'd be for your husband.

Some in the comment section have suggested bariatric surgery but this is an awful and unsustainable option as well. Effectively, your husband is far more likely to have his lifespan cut short if he was to have the surgery, and would have to live with debilitating complications for the rest of his much shorter life. At best it's a cosmetic procedure that doesn't actually make him healthier and at worst is far more likely to lead to a premature death than his weight ever will. Please, please PLEASE do not pressure your husband to undergo it.

Ultimately, I think if your husband's health is truly your number one priority, it is worth investing in educating yourself. I can recommend some basic things to start with. For books, start with Body Respect by Linda Bacon and Lucy Aphramor. For social media, start with Dr Joshua Wolrich and Your Fat Friend. Bacon, Aphramor, and Wolrich are all health professionals who will be better able to explain the actual nuance of both the relationship between fat and health, and deconstruct the complexity of the social determinants of health. It'll help you to determine which battles are worth picking and why. Your Fat Friend writes essays about the experience of being a fat person that might help you build insight into your husband's own lived experiences and critically process your resentment. This will be crucial for your husband's mental health, which is one of the main social determinants of health