I know a couple who do this and get carers allowance. Very difficult to do.
One has learning disabilities but is physically fit and can, when prompted a lot, manage to do various things, the other is physically disabled.
It was horrendously hard for them to claim though because though they weren't called lying bitches they were accused of benefit fraud for claiming. I live somewhere with no representation at appeals and they won theirs, eventually, and the judge was appalled they both had their PIP and ESA stopped simply because they applied - they were reported by the person doing one of the assessments for committing fraud (ESA is paid couples rate so was stopped for both). It's quite obvious when you see/speak to them and how they work together how carers allowance can be paid without breaking any rules. However, on paper (or on a screen) it is less so.
They also get extra help as well.
At PIP renewal I'm sure it'll happen again.
I've been reported by cpns (they told me they were doing so) for being allowed high rate care because ten years prior I was capable of working in a managerial position upstairs and have degrees, and that's happened more than once. HOWEVER and I know this is rare, but DWP sided with me, literally I got a letter within a couple of weeks saying there had been a malicious report. That was it. The cpn then discharged me.