That's very sweet, Bluebell. We too have a friend with dementia and we do just as you describe, just KBO (keep b*gg*ring on) with him. And it does produce its funny moments! When he was still driving he moved their car away from the house for a work truck to be parked. Unfortunately, he couldn't remember where he had parked it and my Dh had to go and look for it! As his wife says, if you don't laugh at it, you'd cry.
Parents-in-Law. What do/did you call them?