It looks like these seats, if they are truly Pacifica units, bolt to the pedestal that actually guides the seat down into the well. So the attachment is probably to the pedestal rather than the van body. A collision shop might know the details as well as the dealer. But I don't really see any attachment points on the shot of the underside.
Also, there seems to be an electrical connection -- these are possibly heated seats.
The e-bay company is well rated, but two flags on this item for me -- it says "Warranty - yes" (how? who?) I don't think Chrysler is interested in supporting seats that were removed from another van. The other is they are flogging them as appropriate for a range of vehicles "Easy can be installed in any Jeep , Car , Truck , Classic Car , Hotrod , Van , Bus , Boat , ..." Just seems too universal, but what do I know? Chrysler may have standardized seat frames -- helps with inventory.
If you do undertake it, heed 94044's warning about springs under tension. I remember being caught unawares folding down the back of my 2008 Stow & Go -- almost gave me a concussion because it snapped down so fast.
2017 Pacifica Touring L Plus
Build date Oct 2016 - Delivered 11/30/16