Well, based on the numbers provided by the OP...
2018 Expedition
Curb Wt: 5,623
GVWR: 7,450
GCWR: 15,200
Therefore, the payload of that vehicle is 1827.
We also have a family of 5, and while my trailer is a tad heavier, I know we're using every pound of my Suburban's 2088-lb payload.
My concerns are more general, in the sense that as you get closer to the max ratings of a half-ton, stuff starts to break. Semifloater axles aren't as forgiving of being overloaded/heavily loaded compared to full floaters.
What kind of towing? Long hauls cross country, or mostly shorter trips? Shorter trips, you'd probably be fine, but if you're talking about cross-country, long trips, I'd be concerned about the durability of the truck. Ask me about my "unscheduled" four-day visit in Mitchell, SD and the Corn Palace, with my heavily-loaded half-ton TV.
