I think what is happening is you do end up with 2 drivers on the same train; the second one will lose all his or her commands. You don't say which of Bald's commands is the one where the coupling process starts.
For this to work the "Drive to red circle trackmark" must be the last in Bald's sequence. Similarly, the "couple to" command must be the last in Guriga's sequence.
The first "Check Consist" Rule (checks for consist with all 3 locos) then adds more commands to Bald's sequence, the first is decouple the last vehicle; the rest can be anything you like. The 2nd Check Consist Rule (checks for just the single loco on its own) adds the rest of the commands to Guriga's schedule.
In your screenshot you don't have any more rules as child rules of the 2nd check consist rule.
I think that must be where you are going wrong.
Actually I quite like Stagecoach's solution. It is better, as it doesn't involve session rules, but not so elegant as you will need an invisible train on invisible track.
Edit: Try this "session 3" for a version of Stagecoach's idea, with messages. It should be obvious which is supposed to be the invisible train...
https://www.dropbox.com/s/50ayt07y88gv8w5/Lumber test session 3.cdp?dl=0