We've just got the one child, but she can be as much a handful as two at times. We do our best to wear her out before it's bedtime. Generally, that's my department, and while I'm with Katie, Lena gets the bunk set up. Then, there is absolutely no eating or drinking inside Snugglebug for all children - specifically, Katie. Sometimes we let her watch a DVD while she settles down in her bunk, but once the Nichole guard goes up, there will be no little feet coming over to tickle our faces.
We also borrow Kate's cousins as playmates from time to time. My 7-year-old neice does fine in the other bunk, my not my 5-year-old nephew. He's got a snore twice his size and will not be making another appearance in Snugglebug. :sleep::sleep:
Having small children cooped up in a small space certainly could have the potential to turn into a disaster. We wouldn't take Kate with us for a rainy weekend, it would just be asking too much of a 6-year-old child. It takes a bit of planning, and sometimes the proper motivation to keep things running smoothly (promise of reward... and fear of punishment).
If you are taking the grandkids out, I'd hope that Mom and Dad have taught them to respect your word. Otherwise, you might have a lot of ground to cover in a short time.

I would suggest that spending the night in the trailer should be treated as a huge priviledge - not a certainty. And there's always the promise of a special treat or event in the morning for little ones that behave (go to sleep) at night. If you are planning a long trip it might be a good idea to do a trial run night.
Hope this helps,