Ok, here's how I got the two locos working in the way that Bloodnok described in his post.
Here's the map of the layout, broken into 2 parts so that it complies with allowed screen sizes on this forum

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The green T's are obviously Triggers and the red dots are Trackmarks, and most of these should have their radii set to between 5 and 10 (although trial and error with their positions will also get the results you want).
Don't worry about the radii for the moment. Leave that for when everything else is set up and the locos get stuck for some reason.
Make sure to put buffer stops at the end of the stabling spur, and also at the end of both prongs of the "Y".
Now, if you've added all the trackmarks and triggers and named them, and you've added loco 1 with a few carriages and loco 2 in the correct place, you should edit the session and add the following commands to them.
Alastair (Loco 1)
>> Drive to Station
>> Load
>> Uncouplez
>> Wait for Trigger "clear" to be triggered by "loco 2" // waits for other loco to collect coaches and pull clear of the station
>> Drive to Trackmark "stable" // drives this loco into the stabling point out of the way
>> Wait for Trigger "arrive" to be triggered by "loco 2" // waits for the other loco to arrive back at the station
>> wait 20 seconds // just to give the train at the platform enough time to load passengers and uncouple
>> Couple at Trackmark "couple" // drives this loco up to the trackmark "couple" and couples up to the carriages in the process
>> Drive to Trackmark 1 // see next command
>> Drive to trackmark 2 // This command and the previous one use the "Y" to turn the train around so that it pulls into the station loco first.
>> Repeat // don't forget to add the repeat command
Adair (Loco 2)
>> Wait for Trigger "arrive" to be triggered by "loco 1" // waits for the other loco to arrive back at the station
>> wait 20 seconds // just to give the train at the platform enough time to load passengers and uncouple
>> Couple at Trackmark "couple" // drives this loco up to the trackmark "couple" and couples up to the carriages in the process
>> Drive to Trackmark 1 // see next command
>> Drive to trackmark 2 // This command and the previous one use the "Y" to turn the train around so that it pulls into the station loco first.
>> Drive to Station
>> Load
>> Uncouplez
>> Wait for Trigger "clear" to be triggered by "loco 1" // waits for other loco to collect coaches and pull clear of the station
>> Drive to Trackmark "stable" // drives this loco into the stabling point out of the way
>> Repeat // don't forget to add the repeat command
Now, you should be able to run this session and watch as one train pulls into the station with a few carriages, opens it's doors to load/unload, closes it's doors, and uncouples.
Then the train in the stabling area will come and collect the coaches, and leave the station with them. Once the line is clear, the loco that's left in the station will pull into the stabling area and wait for the train to return with the carriages.
This process continues indefintely, with the locos taking it in turns to do each job.
If you have problems, you should probably make sure that the "stable" trackmark isn't too close to the buffers at the end of the stable point, otherwise it may never reach the trackmark area.
You should also be aware that certain signalling may stop this working.
As a test you should place a signal in the stable spur, that in proto situations would keep the loco in there until it is safe to leave.
This will probably stop the session from working, as the loco in there isn't able to pass the signal when using the "couple at trackmark" command.
Removing the signal allows the session to work, and doesn't really take anything away from the layout.
That should be it.
There should be enough info there to set up any amount of automatic traffic that you want on your layouts.
BTW Ian, you don't need the Change Direction command like I said you did in the Email.
I usually use it because the AI easily gets confused with automatic operations, but this example is simple enough that the AI seems to cope with it.
It's still one of the 4 "must-have" commands for auto running, IMO.
They are "UnCouplez", "UnCouplezFrom", "Couple at Trackmark", and "Change Direction".
Good luck,
Smiley.