To the OP I will add this regarding the KZ2505. The front storage area is great...but it raises the floor in the bunk room. Therefore your still growing child who is 5'9; will have ZERO headroom up there. My oldest is 5'3" and she finds the lack of headroom in the front bunk area to be very lacking. I would go take a look at this trailer and have your kids check out the bunk area. If all theyre going to do is sleep up there then it wont be a big issue. The old Outback 26RS is identical but keeps the floor in the bunk room even with the rest of the trailer and gives you headroom equal to that in the rest of the trailer.
My KZ was weighed coming home from a trip and tipped the scales at 5200lbs. Id say that weight may have fluctuated and probably could have been in the 5500 range at times. The tongue weight was also weighed and if I recall was around 650.
I towed with a Dodge Ram for a few years and they have lower payloads than other half tons. I was within 200 lbs of my rear axle rating, but well under my trucks towing capacity. I ended up storing some stuff- loaded cooler, portable grill, inside the trailer to give some more cushion to the rear axle rating.
Like I said in my earlier post, a properly equipped Suburban, Expedition (EL) Crew-Cab pickup or as some have mentioned full sized van should pull the KZ just fine as long as you stay within your limits and pack wisely.