For posterity, I’ll record here the method that I ended up using: At the Content Browser, I added a new Blueprint Class of type AnimNotifyState, and in there I made references to the other mesh so I could get access to their trails and start them/stop them as required.
Then it just became a matter of putting the AnimNotifyState at the desired points in the original animation montage.
Hopefully this will help others with the same problem as me.