Hi, I have an idea for a a way around this problem.

You could create 3 rail signals just to the left of the 3 train stops that are working (so, 9 signals total). They could be somewhere along the straight where the trains naturally park anyway.
These signals need to be changed to Red via circuit ...

When the path includes a train stop that is not the destination -> Add a penalty of 2000.

So basically.. waiting at the signal for another train to leave is cheaper than routing through a train stop that's not on the schedule. Maybe this penalty can be applied only after a certain distance?

Added a screenshot from my current game. There are two stations free in the "depot", but are not utilized. The chain signal is not sending them through. If this is intended i guess i have to find a better place to unload the crude oil...

Given a train track which branches 3 times and all 3 branches looping back into each other by a single track.
All 3 branches have a train station with the name A.
On the single track, create a station B.
After the first branch off, create a station C, so that trains going to A2 and A3 have to pass ...