can a group that have 700i follow each other in case we get separated?

AFAIK, there is no such feature on personal accounts (the kind of account most of us have). I don't know anything about enterprise accounts.

There are, however, iR to iR messaging features that can help. For example, you can use the device to navigate to the location from which a message was sent to you. Messages do show up on the map, so you can also see the location from which the message was sent. (In challenging conditions, I believe this is the location from which the sending device initiated the message, not the actual location from which it was finally sent. If the device is moving, the location from which it was finally sent may be quite a distance from the location where the message was initiated. You want the initiating location.)

No, such feature, as on Tread and Zumo XT introduced, does not exist on Montana 700 series.