It's funny that I'm reading this thread now... I've just got done sharing our camper with my in-laws for one night this past weekend. So a total of 6 of us for one a day and a night. The day and evening was not an issue - we were all outside doing camping stuff (LOL) late in the evening the kids went in and were in bed before the grandparents joined us inside... We ended up sleeping in the bunkhouse with the kids and gave the queen up front to Grandma and Grandpa.
Long story short - for one night it worked for us - this time. We are a very close family and it was no issue. However... If it had been a really rainiy day, if somebody wasnt feeling well, if i would have needed to cook inside... I don't think I'd want to do it like this for a longer trip. Even a camper the size of mine closes up really quick.
We are going to camp with some friends in a few weeks - and they are bringing their own camper in the site next to us. It will be our first time camping as a little group and I'm really looking forward to it. But - with the knowledge that we all have our own space!
OP: Thanks for sharing your story. Sorry it was rough. I think you got good advise to take the DW out on your own - just your family and I think it will go better. And... Also good point made - we always end up laughing most about the things that go awry.