Large family problem (we are 8)

I would look at Travel Trailers with bunk houses, (extra bunks). I would consider a 1 ton passenger van for a tow vehicle. Some of them can seat up to 12.

Go to a dealer, or look on line. There are hundreds of campers that your family can easily sleep in. Mine sleeps 10.

However. you will need more truck, as all those people will take up ALL of your GVWR, and tow capacity. 3/4 ton, or 1 ton van would prolly be best, OR take 2 vehicles

Depending on the age of the kids a viable option to sleep so many is use a nice tent and make an adventure out of it so they want to sleep in a tent.

You might also consider a hybrid trailer. The pop-out beds will sleep 2 people each.

If you have older children, they might be just as happy to sleep in a tent out back. They would still have access to the RV amenities and be close by. I see people doing this a lot with families.

My mother's family went camping several times a year with a family of 11 but they used tents. We did the same with four children.

Our Outback sleeps ten but it would not live ten. We put up a tent to sleep children who are old enough. We can hang cheap, lightweight tarps from the awning to make an extra room.

Your problem will be running low on GVWR on the Expeition before you hook up the trailer and add its tongue weight.
You'll have to watch weights very closely.

You are probably going to be happier and cheaper by using two vehicles. One for most of the family and day trips while camping. Another to pull the rig.

You really can't get a decent sized camper with enough beds and some floor space for everyone for a weight that could be pulled those vehicles.

We were a large family growing up, went to the lake every weekend possible in the summer, slept in lawn chairs initially, finally got a tent between my junior and senior year of high school.

Looking back on it fifty years later, my sisters and brothers and I say it was the best time of our lives. Camping is a wonderful way for a family to grow up.

But it was a logistical PITA for my parents, that got a lot easier when they started taking two vehicles.

I agree with much of the advice so far. Take your time and do not buy a vehicle until you understand what type/weight range of RV you want.

You can almost ignore tow ratings with large families and RVing. I would throw that Expedition off your list. Some families of 8 exceed the payload/GVWR without towing a trailer! The NV3500 has the specs/ratings for up to maybe 6500 pound dry RV and a large family, although I'm not impressed with the engine/trans. Two vehicles especially since you probably already have a daily driver with 8+ seats is a reasonable approach if your trips are say less than 4 hours each way. A 1-ton GM van is a good value as well, for up to around 7500 pounds dry TT.

The van will be more effective than the expedition; you have more payload capacity in a full-sized van. Conceivably a Chevy or Ford E-series might be able to be configured for a little more carrying capacity than the Nissan, but I'd much rather ride in the Nissan than one of those for a long distance, thanks to the much nicer seats in the NV (and the ability to space them out for more legroom if you don't need all twelve).

You might also look at motorhomes. My class C can theoretically sleep eight and has seat belts for nine (which may be of questionable effectiveness in a serious crash), although with that many people there is not a lot of weight capacity left for food or water or stuff. You could also tow a small travel trailer or popup behind most motorhomes pretty easily. There are definite advantages to traveling in a motorhome vs. a van or something else, such as having ready access to snacks and books and a restroom.

Stop paying attention to tow capacity. Concentrate on payload.