Thanks for your replies; it took a while till this was permitted by the admins (first post) and I didn't know that there wouldn't be an email notification. My bad, should've checked more frequently. So, sorry I only got round to replying almost a week later.

I guess you confirmed what I kinda feared and perhaps knew. Should perhaps have clarified, the house is cleaned up (now), he's just not pulling his weight in maintaining the household. There's stuff that's accumulated over the years (his stroke was 2 years ago and his negative sides have been amplified); now he's completely negligent when it comes to cleaning up or in some ways even dressing properly. As well as refusal to undertake things that would penetrate his comfort zone - there are alternative means of addressing underlying health issues, e.g. through herbs from TCM I got from my girlfriend's dad who's from Asia which he refused to take because "they didn't taste good and he can't have sugar with it." So, effectively, it's upon the rest of us to tidy up. His work he can do alright, his speech is fine as long as he concentrates (interrim manager, currently lots of phone conferences, his speech is alright) - just a lack of movement.

The threat to themselves or others is a legal means that exists where I live as well, but he's far from that. Legally speaking at least; he doesn't threaten anyone nor does he become outright violent, he's thankfully got that self-control, Technically speaking, it's a slow suicide through eating the wrong stuff, not getting exercise and shutting out uncomfortable social matters as well as his past. Any argument ends in him sulking like a child, becoming an outright drama queen and leaving the room.

@unaluna As to lightening the load/helping day-to-day, I don't think it's a good idea - from care of children to the elderly, I've heard it said time and again "let them do what they can do, even if it takes ages." So, any physical exercise he's required to do I won't take from him, be it walking the dogs or tending to the horses. Did that from the start at the hospital, requiring him to talk form day 1 and not making anything easier for him. I think that's the problem I in particular have - our intervention got him this far, there must be something that's missed. I perceive this encouragement as an exchange for all he's done for him, which is a lot. Hence my refusal to give up. I feel like if I took over more things, he'd give in to sloth, as well as it souring relations even further with my mum who'd probably give him the boot at some point.

@sarahsweets I'm so sorry to hear about your son. His stroke was in 2018; problematically, given his, well, inactivity, getting him to do any therapy is near impossible. He had speech therapy as part of rehab and some time following it (also basically ever since day 1 in hospital through us); the speech therapist said he was fine and if you don't know him (or know certain signs) you wouldn't hear it. So, given this "sloth" I think psychotherapy would be preferable right now. Is there a particular reason you suggested this order?

@CANDC&quietlylost thanks for the links and book tips. I'll need to check whether services of the kind, i.e. are available in my country; I'd contemplated researching them out but figured most things are restricted our cancelled given the current virus situation. One of the reasons why I'm on this forum instead. The boundary advice is pretty good; I am I guess fortunate that I've got extended experience with my girlfriend who's got her own mental issues., so boundaries have been firmly drawn. Interestingly, she's had a breakthrough in realisation through an offhand comment I made and had made multiple times before. Probably an example of "right time, right place"; it's led her to move forward with her problems. So, in staying with leverage as pointed out by CANDC, I guess his sister might be the right one. Maybe such a "lucky punch" can be landed as well, even if unlikely. It's weird what leads people to realisations sometimes - which is why I feel there's something missing. Else, it's probably just being there and offering help if it's wanted.

Anyway, thanks again for all responses and advice :-)