They sound nuts - and I say this as a person who has five dogs, doesn't have nice things because.. the dogs... and became a dog trainer/behaviourist because .. the dogs..
It would be unreasonable to invite someone knowing they have a dog they need to bring, and to expect the dog to stay outside - dogs used to living in the house with people almost certainly won't just laze around outside quietly but would kick up a massive fuss, bark and dig and howl and scratch at the door..
But there is a WORLD of difference in expecting the dog to be allowed inside ... and expecting the dog to be allowed to make a bloody mess and take over someone elses house and life for the duration of the visit.
If I go visiting with some of my dogs (I never take FIVE dogs to someones house though!) the two things I can't compromise on are, dogs have to be in the house with me, dogs have to sleep in the room I am sleeping in.
Thats because thats the norm at home and to change it in a strange place would cause more trouble than it's worth.
Beyond that, its my job to ensure my dogs are polite and unobtrusive house guests.
It is ENTIRELY possible to allow your dogs to do something in YOUR home, that you wouldn't allow elsewhere.
My dogs get food scraps off my plate (well I pick it up and give it to them!) - but they know to get this they have to be laid down far away from me, furthest dog away from me gets the goodies first!
They don't get that anywhere but at home, and we eat out at pubs with them regularly where they have learned they don't get anything until we are done and plates taken away.
At home they get on the furniture - if no ones on it they just get up, if a person is on they ask, and they have to get off if asked - visiting other homes they don't get on furniture unless invited.
Does require training though.. sounds like the PIL haven't bothered with this!