Is it possible to put a third row seat in any of these models of jeeps?

If it is the smaller sized (XJ Series) Jeep, doubtful. It would be hard to get them in and out, you'd likely have them facing rear, and entering/exiting through the tailgate. Even the older full size Grand Wagoneer, the rear cargo area is much higher, there would be no foot room, and again, egress would be through the tailgate. Not exactly safe. The older Grand Wagoneer did have a bench seat in front, which would accommodate three people, especially if one is a child. However, the full size Grand Wagoneers are over 30 years old, and they were gas hogs.