If you have all 8 of you travelling to the campground, you'll have to either take 2 vehicles or have a 1 ton-based van (like a Ford E350) with enough belted seating positions to handle that many passengers and still have enough payload capability to tow a good sized trailer.
As for the camper, sleeping 8 is a big challenge, especially if they are mostly adult sized. I know many people love their bunkhouses and they are fine for young children, but once they hit their teens the bunks become too small, especially if they are the 26" wide variety. When our kids hit their teens we opted to go with a U shaped dinette and air mattresses on the pull out couch and the floor. We looked at the double sized bunks but they were just too short to be usable. However, we only had to accommodate 3 teenage boys, far shy of what you're looking to do.
I wonder if opting for a toy hauler might be an option to get extra space to sleep everyone. Either that or 2 campers with 2 vehicles including one that you'd be prepared to drive, or one of your eldest kids?
Good luck with your decision. I hope you're able to find a way to get everyone out camping. It's a great family activity.
2019 Rockwood Signature Ultra Lite 8290BS, B&W Patriot 18K
2016 Ford F-250 XLT SuperCrew, 6.2L, 4x4, 6'9" bed, 3.73
2011 Rockwood Signature Ultra Lite 8293SS (2015 - 2018)