What the actual f*ck indeed.
But though the use of force always seem excessive on an elderly, especially an elderly in a care house, with an amputated leg, stuck in a wheelchair, apparently not his entire head, etc... the man was still holding a "noif" and had "poked" someone in the belly with it.
A knife wound happens very quickly and is can be life-threatening as well, it really does not require much.
Considering the room, small, cramped, etc... the PCs didn't have much options either to circumvent the man either.
So, there is that.
Lots of things could have been done differently I guess, but that's from the comfort of retrospect. Time for Britain to go on developing anti-"noif"/stab suits I suppose, considering how "noives" are the prevalent issue at the moment.
The wear chain mail shirts in Germany, on special occasions.