Is the dog invited?

But they have their dog too, so you are going to have a conversation with them.
You want them but not their dog. Either you accept their dog too, or you tell them to just drive past and go home.
A compromise could be just a day visit somewhere in a dog friendly place.

Why? They know that you know that they have a dog. If your are stopping the dog from going to your house, you need to make that clear. Otherwise it's a reasonable assumption that you don't have a problem with it.

Oh I dunno, put it in a kennel?!

Were they invited to stay by you/your husband?

Why would they think the invite doesn't include their dog when they are on holiday with the dog? Where do you think it will disappear to when they are at yours? Why would you think they wouldn't have the dog with them on a UK holiday? Most dog owners take their dogs on UK holidays, so if they were invited, or even if it was they who asked to stay, and they made it clear that they are on their way back from holiday, you should have made it clear the dog wasn't invited at the time.

Then OP needs to use her words and tell them to go straight home and not visit her.

Kennels are not like hotels. You can't just ring a random one and book a dog in.

I love dogs but would never be happy with an unexpected dog staying. Do you have a secured room it can stay in at night? Will they expect it to stay in their room? Could it be trusted if you all went out for the evening not to destroy your home?

Maybe they thought you knew that they had the dog on holiday with them.And it's just unfortunate that you didn't know. You can either man up and just tell them that you've seen they've got the dog now, and you didn't realise, and you haven't got the space or you can say, you just don't want it there, or you can just live with it for a couple of days. It doesn't deserve all this drama.

No they aren't, they are dogs. It's not obvious - if it were, we wouldn't have such things as kennels and dog-sitters.

Oh dear! Of course pets are family members.

I don't know anyone who would get a dog & then not bring it in a holiday they were going on in the same country. Why would you get a dog in the first place?

You are clearly very naive about peoples love of their dogs!

And dog owners need to stop being so rude and entitled and assume their dog is welcome everywhere.

I don’t like dogs much and do not allow friends’ dogs in my house at all BUT I do make an exception for my sibling’s dog because they only stop off here every couple of years in the middle of a long journey. My need to see my sibling is greater than my need to de-dog the house afterwards. I think you probably have to suck it up this time, they can always take it out for walks.

The thing is, unlike the ones posting here, decent dog owners would not assume that their dog could come over and stay at someone’s house. They would always check before and plan accordingly. The bad owners get a bad reputation for all of them.

You’re clearly a very forthright person OP so just tell them. Dogs not welcome.

You ring around and see which has space. Done. Easy. You certainly don't inflict your dog on others uninvited. Or you ask that borrow my dog service.

This. Either they go straight home or they come with the dog. I wouldn't assume my dog was ok in anyone's house but if I was coming back from holiday where the dog had been with us, and was invited somewhere on the way home, I'd think that they knew about the dog and were ok with it.

You’re absolutely not being unreasonable and I have a dog who comes with me almost everywhere - I would never ever expect someone to just have her as a houseguest!!

I've read your OP (carefully, lest you hiss 'why does no-one READ THE THREAD at me) and subsequent updates.

Are you as abrupt, combative and prickly in real life as you are in your online communications?

If so, just tell them the dog can't come. I expect they'll be mightily relieved.

I have no idea why anyone would get a dog in the first place!

Stupid comment.

Assuming the holiday is a uk holiday? People usually take their dogs on domestic trips because they like their dogs and they want to be with them.

Sounds like a misunderstanding. They think you’ll be expecting the dog because they have one and you think there will be no dog because they haven’t asked.

No-one’s fault really although I think they should have checked. Bottom line; if you don’t want the dog to stay in your house you’ll need to tell them.

I have dogs and no, I wouldn’t just assume I could bring them to someone’s house, I would always ask.
But op, you know now, so you need to talk to your Brother IN LAW (IRTFT) and tell him no, if you feel so strongly about it and your DH won’t.
As an aside, do you stay at their house, with the dog?