Why not do what the diagram suggests? Use a light spring to hold the switch blades for the required route and let the train push through them, they will just spring back, when not held open by a flange.
If I was an 0 gauge modeller I would be jumping at the bit at those prices. 00 coaches are retailing at around 80 odd quid each! Scratch or kit built 0 gauge coaches have got to be worth a lot more than that!!
Run round the train, shunt the train onto the loop, remove the toad and shunt it into the loco release road, collect the out goings and place them on the toad, and then shunt the incomings.
With roller gauges, you can wind some fine wire in the grooves, to lift the sides of the gauge high enough to allow the foot of the rail to be clear of the gauge. For triangular gauges, file a bit off of the outside ears to allow the rail to twist.
Of the choices, a symmetrical tandem is probably the easiest, similar to the Peco product, handed tandems have too many options which makes getting the 3rd common crossing in quite difficult, especially in 00.