granddaughter sleeping arrangements.

I'd been married a year by 21! bewildred you do not have to like it but really it is not for you to comment directly! The couple are adults, your DD is OK with it.
I was mildly surprised that at house party for a friends 80th her 16 yr old grandson and GF had a room together but if they are already in a sexual relationship better it be open than furtive, comfortable than not
!

Just going to say Elegran that ALL the schools have broken up now!

Didn't we have a conversation on this topic just a week or two ago? www.gransnet.com/forums/grandparenting/1250175-What-would-you-do That pair were only sixteen, but the basic principle of "What are the rules? Who is making them?" applies.

Incidentally, there were suspicions voiced that that thread was a wind-up.

OOOOO tricky! I think I'd just say you are entitled to your opinion but you should probably keep them to yourself. I can only say neither of my daughters expected to have a physical relationship with their partners in our house - they were both able to make 'other arrangements'. That being said can distinctly remember my own escapades whilst engaged!! (we were buying a house and planning a church wedding fgs but somehow nobody expected us to be doing anything other that cuddle!)
I think that the view is that they will enjoy themselves whatever the rules are and perhaps its better to have a place of safety rather than those (now I think about it) alarming incidents in the back of the car in the 1970s!

Nothing to do with you.

I should not worry about it - it is their decision. I can understand you might not be happy if it was a one night stand with some random bloke; but this is her boyfriend.

It is the accepted norm, I would say.
That doesn't mean you have to accept it, but best to keep it to yourself, since it isn't your home.

Perfectly normal , as long as she’s following house rules which it seems she is as her parent says it’s ok then I don’t see a problem with it.
If she were 16/17 I’d think differently.