I am assuming you have the transmitter's dual/steering rate turn up to 100%. Right?

This is just too weird to have two servos do the exact same thing, but your ESC is able to find neutral on both channel one, and channel two. If your ESC is able to find the neutral signal from your transmitter, then your servos will find their center. Do like collector said. Take off the servo horn/arm (leave it off), and with the transmitter's dual rate turned up to the maximum; steering trim set to neutral, turn on the transmitter, and turn on the ESC/receiver. Where your servo's spline is now at, that is now their center. Reattach the servo horn/arm accordingly.