What (if any) ground rules do I need to set?
We're going out for a curry for a family occasion, I'm pleased she agreed to come. I plan to drive and had offered to drop her home so there's no "need" for her to stay.
DS is 20, but basically had no social life because of lockdown for the first 18 months of his adulthood so I haven't faced this before. GF is only 17yo.
So I've asked if it's OK with her parents. I highly doubt that he's checked but that's his /her problem, right? No need for me to check?
I've asked where he expects she will sleep and (obviously) he's thinking in his room. He only has a single bed.
I've suggested he sets up a camp bed, but apparently that's not necessary. In my head it makes things more proper to at least offer her a separate bed, even if it's not used but I understand that's ridiculous 
I know absolutely my parents wouldn't have allowed it, either having a BF in my room or staying over at a BF's when I was 17yo, but they weren't necessarily right.
I'm quite pleased that he wants to bring her here TBH. However, his room is next to mine and I absolutely don't want to hear any goings on!
In a start as you mean to go in basis, what rules do I need to set?
Also, usually with overnight guests I'd get something nice in for breakfast. But this is DS's guest and doewn to him? I don't mind doing it, but don't want to be OTT either.