Simon,
I am not sure if you have or have not solved the problem of wiring your crossings yet, but there is an "error"* in the original diagram. If you look at tjhe "A/B" changeover switch, the Blue and Red feeds are both connected to one common feed. However, they should be connected separately - the "top" red and blue should come from the diagonal road as drawn. However, the bottom red and blue should be connected to the red and blue rails at the toe and of the point. As drawn, you might get a short or no feed depending on how the diagonal road is fed in relation to the feed to the toe of the point.
Hope that makes sense. Although a crossing through a point looks a bit nasty, it is actually no different in principle to any other diamond crossing, and this means that it is sometimes possible to replace the A/B switch by one driven from a suitable point controlling the routing through the crossing (I do this on my layout) but this will not be so if the two routes are completely independent of each other. You also would really need to have full interlocking between your point levers if nasty things are not to happen...
Hope that helps.
Howard
Edit:- * not an error if all the reds and blues are commoned together as Neil suggests in his later post.