I write as someone with Parkinson’s and it is challenging to live with and practically impossible for those trying to help to follow and keep up all of the time. This is at least in part due to the fluctuating nature of the condition which can change even through the course of a day. I tend to think of it as like bouncing a tennis ball on an uneven floor never quite knowing what it’s going to hit or where it’s going to land! As you and your brother are finding, it is not an easy path. Before going on I would stress that what I write is only my view. I don’t know you or your dad and only know of your circumstances what you have written so there’s a lot of reading between the lines which may not be accurate.
First thing I thought is there’s that phrase again - we only want what’s best for dad mum or whoever. Of course you do, as would I if in your shoes but it may be worth thinking about how you are doing it. You and your brother think supported living is the best option for your dad and you may be right. However put yourself in your dad’s shoes. He may see it as you have decided it’s the only option and spend a lot of time trying to persuade him when he is quite capable of making his own mind up thank you very much! He might actually think it a good idea but not now; perhaps he’s not ready to leave the home he shared with his wife for eg. Have you tried to talk to him about what he thinks and feels rather than just trying to persuade him to accept what you and your brother consider is best. It has to be his decision and to do that he needs to acknowledge there are some things he can no longer do reliably and/or safely. Most people would struggle to accept that. It may be worth doing it differently, i call it drip feeding. Keep it low key mention it in passing as and when you can. It takes time and patience but can be far more effective than a head on assault. Box clever and he may well come to agree with you but the most important thing is to understand his view. Personally I don’t take kindly when in trying to help someone takes over - well-meaning certainly but necessary? No. I may be slow and look awkward but I can still do it.
When I read about his anger it made me wonder if he struggles with this as I do. No I don’t get angry in the way you describe but I can become quite irrational over something and then that often becomes stressful. The odd thing is that sometimes I know I am being irrational but all my various coping strategies will suddenly desert me and there’s little I can do about it except let it run its course. Maybe your dad experiences some similar issues with his anger. Is there any pattern to it any subject in particular that sets him off. I know it doesn’t reallly help but do try not to take it personally I doubt there is malice or intention to hurt but on the other hand you may be the only ones he feels safe enough to let rip. You say he has deteriorated and it could in part him struggling to accept this.
Also please remember if he is struggling more to do things it will be physically and mentally harder, take more effort and be absolutely exhausting. Many people don’t understand just how tiring living with Parkinson’s can be nor that it is not your average fatigue. Throughout the day we have to give conscious thought to things you just do like stand up from a chair or walk across the room
I kno2w this is of little practical use to you but perhaps it will give you some way of viewing your dad’s reactions a bit differently. You want what’s best for your dad. In my book you are already doing that by being there for him along with your brother and doing the best you can that’s all you can do. Fact is at the moment he is able to make his own decisions and you may not agree but it is his decision. Perhaps it is worth noqt mentioning assisted living for a few weeks or as I say, keep it low key and be patient, he may surprise you yet.
Good luck and best wishes - you are doing alright you know just hang on in there