If you move back to the UK, both you and your husband will be entitled to NHS care immediately. There should not be any issues related to having lived abroad. I used to live in Canada, and have contributed for years to an Expat forum. This issue comes up frequently, so I’m quite confident that you won’t have a problem.
You have doubts about the quality of NHS Parkinson’s treatment. From what I’ve observed, NHS care for Parkinson’s is a bit of a post code lottery, but is generally good. Based on my own experience, the biggest difficulty you are likely to find is a long wait to see a consultant. In the end I chose the private option. My private neurologist cost £250 for the first consultation, and £130 for each 6 monthly check up. Apart from that I get the drugs and physiotherapy free on the NHS.
Having moved back, you could sell your house and buy something more suitable, but I realise that is easy to say and more difficult to do. You can get help from Social Services to adapt your home. I’ve had that done twice for both my parents and each time it was free. They will usually lend you equipment too.
Arranging care for your husband may be the biggest challenge of all. There are a number of different options for care. The one you describe, which sounds like sheltered accommodation with extra care is probably one of the more expensive. Carers can come to your home. That is probably the cheapest option, if night care is not needed. My father who had Lewy bodies was looked after by my mother at home, with the help of carers, until his death.
If you bring your husband back to the UK, you should waste no time in getting a Social Services assessment of your husband’s needs. Even if you do not qualify for any financial assistance, the advice of the social worker will be invaluable and put you in touch with agencies which can help you.
State aid for care is available, but it is means tested. There was a similar case to yours on the expat forum and the value of the house in France was taken into account in the means test, meaning the family did not qualify for state aid. This will become a major issue for you if your husband deteriorates so much he needs residential care. You should probably get some advice about this from Age UK or the Citizens Advice Bureau, but you should probably be thinking of selling the house in France.
Best of luck to you. The road ahead of you must appear daunting.