Best tow vehicle for family of 6?

Ram 3500 megacab with cummins diesel. Cab is huge and if dually will tow just about anything you buy now and in the future.

While the manufacturer may state a certain weight can be towed it does not get rid of the other limitations. These limitations are found on the drivers side door frame
Namely the GVWR (payload capacity) which is how much weight you can stuff into or onto the tow vehicle SAFELY. 10- 15% of your trailer weight will be transferred to the tow vehicle reducing that capacity.You must include all passengers, pets, diapers anything that goes into the vehicle. Do not exceed this number

Then there is the Combined weight GCWR which is the sum of the weight of the trailer, weight of the tow vehicle, all passengers, cargo, supplies etc. Do not exceed this number.

Then you can consider what the vehicle is rated to tow.

Now you are really confused

Not knowing much on vans I would look at 3\4 ton vans or a camper within the limits of a Denali

A GM 3500 Express or Savanna van with the 6 liter and 6 sp transmission. Not only will it haul a trailer, when you want to take friends and family, it is a 12 seat fun bus.

They are great deals buying off-rental. You will need to watch for their availability, as they seem to come off rental when the companies can replace them.

99-2003 Ford Excursion with a 7.3 diesel if you can find one.

The Yukon Denali does not have an 8900 pound tow rating. For RVing, the receiver limit of 1000 pounds or payload of 1400-ish pounds will be the limiting factors. 1000 pound TS is about 7500 pounds loaded and your family then should weigh under that remaining payload of 400.

There are used 3/4 ton Suburbans, but those were lat made in 2013. Otherwise, 1-ton passenger vans work well. GM and Nissan make them still.

A full size van?

Another option, Custom Autos by Tim.

How old are the 3 kids? If one is old enough to sit up from, you can order a type of bench seat for the front that seats 3. But that's a bit of a risk with the whole airbag explosion danger. Actually I wonder what kind of protection the person sitting in the front center has since the two front airbags are primarily for the driver and right side passenger.

Crew cab 3/4 or 1 ton pick up.

Just sitting here watching Diesel Brothers on TV. They make 6 door pickups.
But I wouldn't think you're serious about that as a tow rig option. Based on your post it doesn't sound like you to have the biggest most ridiculous truck in the subdivision. Besides, your HOA might have you thrown in jail if you bring one of them home, lol.
If you're into dumping big money to haul a gaggle of kids and a big trailer and not satisfied with an older used 3-4 ton SUV or a van, then I'd spend a foolish amount of money on a Duraburb before a 6 door truck.