"The elderly widow is a red herring, as she won't be affected, and will continue to be able to have a relative stay over, and so will the disabled person."

I only wish that was true. But the only exception, so far as I aw aware (and I have good reason to be aware) is where there is a live-in career, or equivalent (ie a rota of carers). If I'm wrong I'd be delighted - but that definitely isn't what the guidance stuff produced by the authorities locally says!!!