Thanks again, all.
We arrived at FCO 3.5 hours ahead, as taxi only took 35 minute from near Pantheon (on a Sunday early morning).
We went to Terminal 5. We stood in a shortish line to enter the terminal but were told we needed to wait 30 minutes before entering the terminal and were pointed to wait in a different area. After that we entered and went to check in (some members of our party had checked in online but not all were able to). The line took about 30 minutes and the 2 of our party who had not attempted to check in online (we realized later) were not given seat assignments.
Then went to security. It's a bit of a blur now, but we were shuttled twice I think - the second time to a different terminal to catch the flight and board outside, climbing the steps old fashioned style. I think that was related to the fire and not the airline.
It all seemed like it was going essentially ok, a slow but ordered process. We did take off some 45 minutes late. The flight was fine for me; I don't typically care about the entertainment. Service onboard was efficient.
When we landed in Montreal however, we encountered poor service through customs and with Rouge. The one and only customs (?) or airline processing gentleman in the connections area seemed ill equipped to handle the very long line of passengers who were running late for connections. 2-3 times he spent several minutes each talking with passengers who were complaining or trying to get ahead in line, further delaying our progress. No additional people were sent to help him (during our 20 or so minutes there - we were near the front). The two members of our party who did not have a seat assignment were initially held up due to an error message on his screen that he did not seem to understand, and then were waived through. We were in a rush to board our connection.
Once downstairs we encountered further issues: the two without seat assignments were ultimately told that the first gentleman had made a mistake waiving them through and they would have to go out to the TICKET Counter to get it straightened out. Clearly, they would miss our connection. Their saga then included multiple people telling them different things, being directed here and there, and finally receiving some help to get on a Delta flight - which when they tried to board were told they could not because it hadn't been paid for! Somehow they were ultimately waived through and boarded with the door closing behind them.
The issues seemed to stem from the lack of seat assignment at FCO, and then some disorganization at Montreal determining what to do about it.
Something to keep in mind.