Thus could have been me two yrs ago! My FIL, also odd, with three hip replacements, started on the dementia route but DH refused to see it. I have never been close to him mysoginistic old bugger but I managed to get him on side with a whole load of sympathy and started batch-cooking him 'ready meals' he could just pop in oven. Then persuaded him to go to GP with DH and me for a "general older person check up". I organised a double length appointment with the most suitable GP and explained the issues to them on phone so he'd be prepared.
FIL talked at length with GP about himself and his ailments. GP very kind, patient and them did an informal memory test, just to give him a baseline from which to detect deterioration in the future. FIL was a borderline pass/fail and was quite agitated about Alzheimer's (GP says this is most old peoples worst nightmare). GP explained simply to him about vascular/other dementia, suggested strategies for coping, talked about the meds he was already on, etc. Also talked about what was down the road. Totally reassured FIL (and us) but made DH realise he couldn't ignore it.
While we were in the surgery, I asked GP if I could be listed as someone that could be contacted about FIL - GP just said to him "is that ok with you?" And he agreed. So now I can order his meds, talk to the receptionists, etc and DH doesn't shoulder all the burden.
2 yrs later and he's degenerated but it's been slow. He had a community Geriatric psych nurse assessment and an EEG to determine if any trace of Alzheimer's; they decided there was a bit. He takes Donepezil which is only licensed for Alzheimer's patients, and it has helped quite a bit. The psych nurse was also brilliant at explaining things about memory and old age.
Today we've been back to doc as he has a start of flu - high temp and chest infection. He isn't good at taking meds so we're now starting down the route of social services organising a carer once a day to help him out. We'd like him to live independently as long as poss, but have to take one day at a time. When he's happy and perky he's lovely to be with (has forgotten how useless women are!!!) and we try to chat most days on phone or in person.
Sorry for the essay, didn't want you to feel as lost as I did for too long without being able to do something to help your FIL out. I help mine not because I'm a saint (as my MIL says!) but because my children need to see how to be compassionate towards the older generation. One day it may be me needing their care! They are also entitled to have a grandad for as long as they can. Sometimes I boss my FIL about but he is grateful! And knows that I am doing it for him. Of course it wouldn't work without DH being supportive too, but he works away several days each week so can't always be there for every crisis like losing the remote control
Good luck
and do PM me if you want to ask or chat. We DILs need to stick together!