Riccarr:
Also, I do believe a DC current flowing in either direction will magnetize the solenoid.
The current direction determines which direction the solenoid pulls/pushes.
Therefore I need to design my 2 wire DC (with forward or reverse current) into the 3 wires of of solenoid pair. I think I can put diodes on each of the 2 main wires to the solenoids, have one diode forward and the other diode in reverse. Then send one of my DC wires to the pair of diodes, and the other DC wire to the common. When the DC goes forward or reverse it should only go through one solenoid or the other. See my attached image as example.
I've yet been able to get the opportunity to wire this up and test it, but the online circuit simulator shows one bulb or the other to light when DC goes one direction or the other.
You're still thinking AC!
Connect the common connection to ground and apply the +ve supply to each of the solenoids in turn. You should be able to get the switch (points in the UK) motor to pull both ways. If not, just reverse one of the solenoid connections so that the opposite end is connected to the common.
12volts will probably be enough to move the solenoids, especially if you connect a hefty capacitor (470uF or more) across the supply. You need to connect a reverse bias diode across each coil to kill the back EMF before it kills your circuit.
You also don't appear to know about 'common ground' wiring. Run a bare copper wire along the underside of your layout (I use a stripped piece of mains cable, 2.52mm cross sectional, I don't know what that is in AWG) and make ALL your ground connections (at both ends) to that. It saves up to 50% of your cabling and pins on multiway plug and socket pairs. You can also connect one side of an independent (not used to supply any other electronics) track supply to it after the DPDT reversing switch, the other side then becomes either +12v or -12v with respect to it, depending on direction of the switch.