Having gone through the death of a grandparent following a stroke, the magic words we had to use were "I think he's in pain." He was well and truly gone by then, but his body was still battling on despite that. Any questions regarding whether we could give him something to let him down easy were met with legally-mandated "no, we can't give him anything... unless you think he's in pain."

It took us a few rounds of this before we cottoned on and completed the dance: "Yes, I think he's in pain."