OP, it sounds to me as though both your parents are entitled to Attendance Allowance. They're essentially caring for one another. (That's what SW said of my parents.). You should be able to use that to buy in extra care for the shortfall?
They may also have an 'underlying' entitlement to Carers' Credit. The underlying entitlement doesn't bring in any money, BUT it does mean that you can get a bit of Pension Credit even when you have decent savings, when there's a married couple involved. I know this sounds farfetched, but different rules apply - at least, that's what we were told.
I can't remember the exact scenario, but the council sent round someone to delve into that for my parents and - to our surprise - we got extra money for them. (It stopped when my dad died. Mum was in a much worse state than him, but she was no longer caring for Dad and the extra stopped, though she still got Attendance Allowance.
Citz Advice might be able to help.
If you already know all this, please ignore.