Fare Enforcement cannot force you to do anything. They will verbally harrass you or hope you think they can make you show them your ID. They may even follow you off the train, but will stop once you leave the station and they see you don't care about them.
Again, unless they are travelling with a deputy. Also, they can call a deputy if they get the itch to, but if you've left the train and the station before that happens, or before the deputy shows up ...
People change cars all the time because of fare enforcement. They will exit the car fare enforcement gets on, then get right back on the train on a different car.
Often, if someone obviously leaves the train when they see fare enforcement get on, fare enforcement will follow them off the train and ask to see their fare. So if a group wants to travel, pay one fare. If fare enforcement gets on, have that one person 'spot' fare enforcement and make an obvious escape off the train. The officers should follow, and then that person can show they paid a fare. In the meantime, the train has left with the rest of the group.