Thanks for all your thoughtful replies. By now of course, our 'little' squabble has blown over.
In the meantime, I read your responses and concur that he's being overprotective, that he feels responsible even though he isn't, and that he's upset and angry, not at me but at the prospect of an uncomfortable situation that he can't control! Judging from these and other posts on Gransnet, such generational conflicts seem to be a universal theme and are not limited to Europe or the Americas. In this case, it's not just about (underage) sex, but that it's being contemplated under parents' own roof.
I wanted to add that my daughter may be conflicted but I also know my SIL and I just can't imagine he would allow that sort of thing ...I am surprised that my Daughter would even entertain the possibility, but no matter how averse we are to this, it is not up to us to make decisions for DD and SIL
So, to put your minds at ease for this round at least, due to current pandemic, DD has reassured me repeatedly, that there will be absolutely NO other house guests allowed during our stay; only us and the four of them.
The King is to resume some duties.
Have any of you got all electric cars? Pros and cons please.
Recommendations please, for a stopover on the way to Loch Tay