Hey,
JAS_OH1, that's a terrible situation. My heart goes out to you, especially as it's not even your son/daughter, but a nephew - and so young. However, it sounds like someone, somewhere has got to convince him that he needs to see a neurologist, a psychiatrist and probably a few others as well. It's either a bloke in denial, or a macho thing, or a "I can manage this"thing - but it sounds serious. How to convince a 30 year old? Can't help there, really. What you've done is great, just absolutely great.
When I arrived in the UK in 2022, my younger brother (who was then 65) was wobbling around, supported by two walking sticks, with bothe ankles and feet swollen. I said : "HEY! What does the doctor say about this? You can't just wobble around and think everything is ok"?
The first reaction was submission (The doctors said there's nothing to be done). The second reaction was frustration (I call the clinic and they don't answer, so I just gave up). The third reaction was mine - I went down to the clinic at 8am the following morning, exaggerated the situation (only a little bit) and by 8.20am, the doc had called and scheduled tests at a major hospital, physio and rehabilitation.
To cut a long story short, I kept bugging him and kept snapping at the NHS. One night he had a crisis (not sure whether it was blood clots, but he was screaming in pain) and we spent 24 hours in a ER until I finally managed to get someone to take some serious action.
The last Hospital visit I got him into was with the top Neurological doctor in King's College hospital, London. The doctor was utterly clinical, extremely sympathetic and incredibly practical. My brother's last 3 months on earth were at least painless.