EDIT: I somehow missed that he already bought a vehicle. But some of the info in my comment might still help someone else. To the OP, solid choice and good luck with the Yukon XL!
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You got some good answers already but here are my thoughts:
Go with a full size suv or a full size van (not a minivan).
We have an Expedition EL with a 2nd row bench, so it seats 8. We have 2 car seats in the 2nd row (middle seat and passenger side seat). We keep the drivers side seat empty so we can fold it down to access the 3rd row, or so that my wife or I can sit next to the kids if needed. But you could definitely fit 3 car seats across.
The issue with standard length SUVs (expedition, sequoia, Tahoe) is there won’t be much cargo space behind the 3rd row. But if there’s only 6 I guess you could fold down part of the 3rd row if it has a split.
But the best bet would be an extended length suv. It will give you a lot more cargo space (expedition EL/MAX, suburban, Yukon xl). I agree you don’t need a Excursion but a suburban or Exp EL would be great. Mine has enough space behind the 3rd row to have a 44qt fridge lengthwise.
But vans are a good too. We were thinking of buying a 15pax E-350 and taking out the last 3 rows of seats and doing a little camper conversion, but we the expedition makes a much better daily driver so we’re sticking with that