Thanks for the comments, Divecontroller. Yes that's the idea, trains will run from either station, do a couple of laps of the main circuit then head into the other station.
In the case of the larger terminus after arrival a station pilot will shunt release the loco from the train and it can head to the loco shed for service/refuelling.
The smaller station has a runaround loop as you describe. The same with freight trains.
This sort of operation was something I couldn't do with my last layout and it was the first thing I wanted to put right!