I have the Life Time Tent trailer the original one which is 4x6 with two queen sized beds on each side of the 4x6 floor. For 4 of us we have plenty of space but pushing to 6 it would be tight. We have a grand parent that tags along occasionally putting us at 5 which case we were putting my youngest in the packnplay across the front of the trailer on the main floor between the two queen beds. Today he's too big! Couple of options I've thought through. Check out Jumping Jack trailers it might be a good compromise you get more sleeping area and given the price for these really nice well done Roof top tents a Jumping Jack trailer is a possible option.
Cot bunk beds pushed to the outer side of the queen bed or across the front of the trailer, thus leaving a sleeping spot for a grand parent and each kid has their own defined sleeping spot reduction in elbow room fights etc. I haven't done this yet but pretty sure I'm going Cot bunk bed system it has far to many pluses to not go that route.
The roof top tent approach I would mount it on a trailer given with that approach you only set up once and can use the truck to go on mini adventures without having to pack it up and set it up again. Lets face it the less set up time and pack up time required with young kids running around the more camping you'll probably do! Not to mention you won't need to remove the tent from the truck during the off season etc.
Keep in mind as the kids get older once they hit about 8-10yrs old you'll want them in their own tent ;-) And they'll probably want to be in their own tent. So keep that in mind vs your investment in the more costly larger set up. Couple of friends with older kids who have really nice hard sided trailers found their kids would rather be in a tent with cots than crashing in the trailer with Mom and Dad. Except for when its really cold out etc.
My rough camping program will be the Life Time Tent trailer rig till the kids hit the point they are not into sharing that space with Mom and Dad. Then my dream would be midsized 4dr pickup with a flatbed FWC. The idea being mom and dad have a escape pod with a heater! And when the kids tag along we can stuff them in the old Life Time trailer. As for gear? The life time trailer and the Jumping Jack trailers give you lots of flexability regarding gear hauling ability be it an ATV, or boats or just lots of crap etc. I roof top our bikes on the Subaru Outback and put gear in heavy target roof top storage bags lashed to the trailer. This approach lets me yank the gear off the trailer pretty fast just unstrap the bags and pull them off set the trailer up and put the kids incharge of hauling stuff into the trailer / tent etc.
When we go big we take the Sequoia example I rack our 14ft sailboat on the top cross bars tall side mode of the trailer, I have two 1/4 ply sheets I lay over the tent which on the floor of the trailer then I pack stuff like our 9ft Avon, tables, ice chests all that stuff etc, bikes go up on the roof of the truck.