I have only read your posts OP so am probably just echoing other people here, but this in your OP seems to encapsulate the whole thing to me:
"Ds has said to.me.why is dh like this ( withdrawn on phone) and i feel.stuck between the need to support ds and dh s wish to help him but the fact that this is coupled with tiredness and occasional ( what feels like resenment/ anger/ wanting freedom from supporting adult dc/ occasional pride in it. Its as if the wants tohelp ds but is tired and is starting to resent it at the same time. I dont want either dh or ds to feel bad . Plus we have said we will help.ds and the last thing i want is for ds to feel bad about it."
Your son is 26. He asked you why his dad was withdrawn on the phone, and it sounds to me that you did not answer your son's question so that he wouldn't 'feel bad'? Given that your husband has "said to ds he is looking forward to the time he can work less" he really shouldn't have to ask - should he? He already knows, really.
Frankly, at 26 he should have worked it out for himself that he's getting a LOT of financial support from his parents, and he should have worked out for himself that since his dad has actually retired but it still putting in 30ish hours/week in a minimum-wage job - maybe his parents are struggling to provide that level of financial support.
Is your son inclined to shove his head in the sand? Because as I've said, he really should be aware of the financial pressure he is putting on you and your husband. What steps has he taken to finance himself? Yes he is working five days a week, but he has evenings and weekends, no? Has the idea that he could do a second job never been raised? Hospitality is crying out for employees right now, which means evening and weekend bar work, for example, is available. My DS, 23, is doing just that. Why isn't yours? Why is he instead just sitting back and letting his parents fund him from their minimum-wage jobs?
Your son sounds very passive in all this, leaving it to you and your husband. Why wouldn't your husband feel resentful about that? And I also have to ask - what do you feel about continuing in "a physically hard cleaning job" with your health issues to finance your son? Because rationally, you too should feel resentment. Your husband has stopped you for working more because of your health issues, it sounds to me as if he'd rather you didn't work at all but financially you have to - and I expect your husband resents that! (As my dad would.)
I guess I'm trying to say that it is perfectly rational for your husband to resent
this situation, resent it for his own sake and also for the burden placed on his wife. And maybe, instead of you worrying about your son 'feeling bad' (no evidence that he would, in my opinion), you should stop infantilising your son and back up your husband and point out to your 26-year-old son that he needs to step up a bit more because you and his dad just cannot do this any longer. He's an adult and he needs to take on adult responsibility. Once he does I would expect the relationship between DH and DS to improve. This financial dependency is the root cause of any problems in the relationship.
Our other dc is about to leave uni and has asked.to.come home for.a while and i think that he is perhaps overwhelmed.
Yes, your husband is feeling overwhelmed. Has your other DC made any indication of what they will be doing once home? Because they need to know that you and your husband are financially struggling and that they cannot just come home , doss, and hoover all the food from the fridge. They might think that's exactly what they can do given how their older sibling is being catered to, but you need to accept right now that you cannot do that and make no offers. Can you do that?