Vans interact at the beginning and the end, and every 6th exchange for about 10-15 minutes. We have had one member from van one jump into van 2 to drive for the last 6 legs just to interact with the other van. Part of the selection on the running order is understanding the dynamics of each van and its members that will be sharing tight quarters in a physically and mentally exhausting state.
Some teams use a rolling seven member van where the active van (runner on the road racing) always has seven and the inactive van has 5 members and they exchange two members back and forth every 6th exchange after exchange 5. These teams get a greater interaction between all 12 team members, but some members take consecutive shifts in the active van which kills any chance for an uninterrupted 90 minute nap.
We stay overnight in Seaside and between dinner, partying, and drving back to PDX, we catch up with each other. HTC is an annual reunion for us and new members of the team quickly become part of the team family. But over multiple races with many of the same team members, you get to know everyone very well over time.