Warning about using a micro switch for on board glow control. I had one plane with it and the radio would twitch or flutter when the contacts closed or opened. Others have not seen this, but I did. Install a capacitor to kill the spark worked.
One problem with only one driver and a parallel connection. The two glow plugs never have the same resisitance and it changes when one engine starts. The result is that one glow plug either does not light or is too dim to help. This means two drivers. Or, if the glow driver will allow it, go to 3volts and wire the engines in series, not parallel.
Good Luck,
Twinman