Speedy, you made some great criteria then seem to have ignored it with your suggestions. Very rational criteria, then some much more fun (except Trailblazer) suggestions. Maybe a left brain vs right brain conflict?
Seriously though, you'll be lucky to even fit three kids into everything but the Trailblazer/9-7X. Going from a minivan to a midsized SUV (like your list above) is going to royally suck. Everything but the Chevy is going to require specialized maintenance, and much more so than the average appliance type car. None of the above are really safe for towing of a 7000 lb boat, my guess is you'll exceed the tow rating on at least a few of your choices. Of the bunch, the Trailblazer/9-7X is the only one that offers a 3rd row seat. But sadly the Trailblazer is a steaming pile of crap that you couldn't pay me to drive. By the way, I don't think any of your choices meet your MPG target. None of those are particularly efficient SUVs.
Seating for 5+, towing 7000 lb and 26', good ground clearance, reliable and easy to repair - you need a domestic or Japanese crew cab truck or full-sized SUV. It will be a hit to your MPG, but I can't think of anything that meets your criteria and MPG requirement. SUV: Chevy Tahoe or Suburban, GMC Yukon, Ford Expedition, Dodge Durango, Toyota Sequoia, Nissan Armada. Trucks would be the Dodge Ram, Chevy Silverado, GMC Sierra, Nissan Titan, Ford F150, Toyota Tundra. On the upside, you can find all of the above for under $20k, though the Toyotas will be higher mileage examples.
I'm actually in a really similar spot, I needed a vehicle to haul our three kids (2, 5, 8) with at least one spare seat, all of their stuff (don't underestimate this one), haul our 4000-ish lb boat, handle the occasional lumber run, and offer 4x4. I ended up with a 2012 F150 XLT SuperCrew 4x4 with the 5.0 V8. MPG is average at 14/19, but it offers a huge backseat for the kiddos, a front bench that gives us one extra seat, we covered the bed with a tonneau cover so it's now a huge trunk, and easily tows our boat. We went with a truck over an SUV because of the bed hauling ability, my house is a work in progress and I hated hauling materials in the back of an SUV. It has worked out very, very well. Our previous vehicle was a Nissan Armada, which was also a fantastic and super reliable SUV and worth considering if you go that route.