To think my son shouldn't share a room with his cousin?

[Sophiehoney]

My husband's sister has two kids the exact same age as my kids, but opposite genders.
They live about two and a half hours away so we see them regularly but not that often. Usually during the Easter, Summer and Christmas Holidays, so about 3 times a year. They stay in MIL's holiday caravan in a nearby site.
The kids and adults all get on great.
This year, DH suggested to them that the kids have a sleepover at ours while they are here, which would be fun for the kids and would give them a night to go out. This was enthusiastically accepted by kids and adults. He has said they can either sleep indoors, sharing bedrooms with our kids or camp in the garden in tents if it stays nice.
I'm very happy with this accept the thing is, DH thinks it would be fine for the two 13 year olds, of opposite genders, to share a bedroom or tent. I'm really uncomfortable with this and think it's a bad idea. I've suggested that the two younger ones share and the older two sleep apart, maybe one on the sofa or something.
DH thinks I'm being weird and paranoid and that they're cousins so it's fine, and I'd be spoiling their fun, but I just think it's inappropriate.
DH says he doesn't know how he's supposed to suggest this to his sister and BIL.
AIBU?

So in your case that was fine, but 13 year olds can have strong sexual feelings and its not as though this boy and girl grew up together like siblings.

I have a boy aged 13 and SIL has a girl aged 13
I have a girl aged 9 and SIL has a boy aged 9

Obviously, the 13yos are closer to each other, and the 9yos are closer to each other.

So DH thinks the two younger ones should sleep in DD's room and the two older ones should sleep in DS's room and that anything else is spoiling their fun and would male the whole sleepover pointless.

I'd stick them all in one tent together. Or I would put the two girls in one room and two boys in another.

Girls together in one room, boys together in the other, if it's a tent I'd let them all share, if it's raining make up a camp in the lounge. The age gap isn't that big.

Chuck them all in together wherever the biggest space is.

Well your DH wouldn’t like it if the 13 year old girl got pregnant…..

DH has never menstruated so…

I’d say exactly this too! The camping would be just as fun for the 9 year olds.

I wouldn’t have them sharing a room. At that age they deserve privacy. I had periods and breasts at 13.

Do you have any specific reason to not trust the 13 yos?

If parents decided to split us with my cousin at the sleepover only because we were the opposite sex, it would make them the first one ever to suggest that sexualised interaction between us was even an option. It would bring something rather awkward to our friendship.

(I was kind of interested in boys in that age, but not in my cousin, he was a family)

The whole point of sleepover is being together.

Maybe they don't want the kind of privacy you'd impose on them.

Similar age gap to one of my sets of cousins and I. At 13 I definitely would have chosen to share with my 9 year old girl cousin over my 13 year old boy cousin.