I'm not sure about all those double slips since on the prototype they would have been an expensive thing to build and install as well as having a high maintenance cost. The guiding rule with signalling is to search out all the paths that will be used through a formation of pointwork and signal those paths accordingly. If you're going to do it with the lower quadrant semaphore signal models in Trainz your job just got harder because there are huge gaps in the signal types available. And just to make it harder some legacy models don't like working with later models.
It might be a bit easier using upper quadrant signals since there is a wider range available, but as a pre-grouping modeller I never use them so I don't know what there is.
Edit: Just a quick comment about your video in your first post. Please don't jerk the camera around so much and keep it steady. The video as it stands is almost impossible to watch or even to understand what you've made actually looks like.
