Michelle, I think you need to tell your relatives to stay in a motel next time they visit. I have dogs. My friends have dogs. I can assure you that I have never smelled a "dog smell" when going into a house where a dog lived except for a woman I used to know who had really serious mental issues and she allowed her dogs to just go in the house and then left it there. Like I said, serious mental issues. Cats, I smell. I can tell even if a person has an indoor/outdoor cat and no litter box. BUT, I would never, ever, ever complain or say anything. How rude that would be.
I'm thinking that you should worry less, and entertain these rude folks not at all. Send them a list of motels and tell them that last time they came for a visit, the dogs complained that the house smelled of rude relatives for weeks afterward.
As an aside, two years ago when I went to visit my sister in Phoenix, it was hotter than blazes middle of the summer. They have a really small house and I was sleeping on a blow up mattress in the floor of the baby's room. They had two cats at that time, and while I was there I ended up rescuing an abandoned kitty that they took in but had to keep in the bathroom while the other two kitties got used to him.
I am allergic to cats. Horribly. And not really fond of them. So for the entire two week visit, when I used the "extra" bathroom (where the cat was housed), I had a kitty in my lap every time I sat on the throne. Yeppers, I peed with a cat on my lap for two weeks. And every night, when the house was quiet and I was drifting off to sleep, the biggest and most bossy of the cats -- a huge male named Mahler -- slunk into the room, climbed up over my feet and settled full length on top of me. He reached from his head on my chest to his feet just above my knees. Huge cat. And started to purr and fell deeply asleep right on top of me. As hot as it was, as hard as my nose ran, there was something comforting about that big old cat on top of me, purring in his sleep. He got up and left just as the house started to move in the morning. My sister couldn't believe he would sleep on top of me. Seems he never, ever would sleep with anyone. I guess I was special. LOL.
Moral of this long shaggy cat story: if these people love you, they won't give a rip if they sniff a little Labrador and they sure won't complain about it.
Sunny -- who is quite rigid about such things