To think it’s inappropriate?

He’s not there to visit your husband.

Why do you want him to book time off work? Would he have done that if his daughter was coming alone?

It is starting to sound like you don’t even want her there.

Yes of course. So presumably her dad will take the time off and spend time with her.

So if everything is closed and she would be bored then surely it’s better for her to have company?

I think you are being unreasonable. It's not really fair to compare from your own daughter who presumably lives with you majority of the time, and therefore would have been able to see boyfriends nearby without the need to stay over? This is a very different situation to that- she lives a few hours away from her Dad and of course he really wants her to come and stay in his home. I know you've described lots of visits, but he's her parent and he wants to relax at home with his child and he's trying to make that more appealing to her actually coming! (Pretty common for teens to want to see their boyfriend at that age I think)
I think it's fine to say he can't sleep in her room but I can see why her Dad is willing to allow it in order to have some time at home with his own child. It doesn't sound like your daughters are in the same situation at all so I think she can have a different rule here without it being unfair to your children.

No way would I condone a 16 year girl shagging in my house.

If she vaped out the window, you wouldn't even know?
Didn't we all smoke out the window when we were teens and cigs stink!

Well that would be entirely unreasonable of you.

The same would apply if she vaped. Presumably as long as she vaped outside or out her bedroom window out of sight of your own kid, it isn't really your concern.

Does she have a bedroom in your house OP? I don't mean a bedroom belonging to someone else which she can use now your older DD has left home but her own actual bedroom that nobody else sleeps in?

How many times has DSD stayed at your house since January OP?

The difference is the other children can see their dad every day and will have a established routine that means that being at home is less boring. For all you know, your youngest might drive and have a car then, so won't be stuck at home.

I agree that I would choose my battles. Just make it clear that agreeing to it for Christmas does not agreeing to it every tim she comes.

I get the 18+ rule and that is what many parents I know, apply.
But if your DSD lives so far away, and you don't have a spare room or a way of moving people around to create a spare room (I assume your DD and DSD don't want to share), then it's pretty limiting to say she can't bring a boyfriend to stay. She can't exactly pop in for coffee with him can she, the way your DD can? Presumably she could bring a best friend with her and she could sleep in her room, but you're saying this man can't.

I also agree your DH was out of order, but unfortunately you are where you are now. It's Christmas, it would be nice if DSD came to stay and spend time in her dad's home, and digging your heels in is possibly going to make it a bigger deal than it needs to be and something that nobody forgets for years.

I don't get this thing about you not knowing him. Surely your DDs brought friends for sleepovers that you hadn't met before? My kids came home from uni with a carful sometimes and it was lovely to meet them. If someone was unacceptably behaved then obviously you'd kick them out, but it's pretty unlikely. Again, it's not DSD fault that she lives so far from her dad. It's reasonable for her to have her bf to stay under the circumstances (and you can maintain the rule for your DD because her circumstances are different).

I would tell DH you're pissed off with him but you're going to be the bigger person and he owes you a nice dinner. Tell DSD if you hear them having sex they're out. Bf has to be considerate with using bathroom etc if sharing with your DD/you. But then I would allow it

I had this scenario with my son with his girlfriend about 6 years ago
At her mother's they shared a bed, when I phoned the mum I told her not under my roof
When they then came to stay
I said to them
She gets the bed
He the sofa
Or
Book yourselves a double elsewhere
They took the former over the latter
If you're not comfortable say so regardless of how 'nice' he is
You can't run with the fox and hunt with the hounds
Rules for the eldest; same for youngest
He's no right to huff and puff it's his way of defence knowing he'd know how you'd feel

Are posters really saying that a 16yr old in a 10 week relationship (is it a relationship after 10 weeks?!) should invite the unknown boyfriend to stay and them sleep together where one of the homeowners is uncomfortable with that? This is the same 16yr old who has also already been in a relationship with a convicted sex offender?

OMG!! Then NO I wouldn’t have any of her boyfriends in my house at all!!

YANBU. Your husband invited someone to stay without even discussing it with you; obviously that's not something that's normal in your relationship or mutually pre-agreed that you both should feel free to do. Even if you agree for the bf to come, YOU shouldn't be expected to entertain him! But I understand how having a strange guest in the house (even one you're convinced is harmless) can be uncomfortable in general. And your follow-up on the sex offender is alarming; husband should take steps to background-check this guy before he comes, and of course be on alert to make sure the other members of the household are safe.

RE the double standard - isn't the boyfriend visiting potentially a different category/scenario - e.g., he's coming to stay as a guest of the family for a few days because he lives too far away to reasonably make day trips? And, of course, he sleeps in the guest room, on the couch, etc., not in SD's room. (And they do what they do, just as your daughter could have done with a local boyfriend stopped in for the afternoon.)

Overall, it sounds like your H is trying to bribe his daughter to visit, probably afraid that if she has to come alone she'll just say no. At 16, being apart from this boy for even a week probably sounds impossible, and maybe she's worried that if she's away he'll move on to someone else. But the reason for her to visit is to spend time with her dad. Boyfriend or no, is he planning to minimise his other responsibilities as much as possible to focus on her during the proposed visit, including perhaps some days out to do things that might be interesting to her?

You don't appear to have shared children so it's really up to the parent to decide what the rules are. You have rules for your DD's and DH has rules for his DD.

I don't see what the issue is of DSD's boyfriend staying - they don't have to share a room and if it's the only way she'll come and spend time with her father then sobeit.

What does dsd's mum think about the arrangement?

Re the fairness and rules thing I 100% agree and you explained it far better than I did., especially your last paragraph. Thank you

How long is this meant to be for? A few days? If so then I'd facilitate. If it's a couple of weeks then no. I would personally like to get an idea of the dynamics between them and check she's alright.

As for the fairness thing. I don't have blanket rules, because my children have different competencies and vulnerabilities. We parent the child we have in front of us. Our kids disagree with us regularly, but they absolutely can't say we have been unthoughtful or inflexible.

I'm not going to make a decision I believe to be wrong because I made the same mistake with an older child.