Ok, this makes me really confused. You are using two yellow motors at 18000 rpm. You are using the orange gear to drop the rpms around 6000rpm. On top of that, you're gearing it down again to the bottom motor around 2000rpm. That motor is going to fight the first one because it wants to go 18k.

And all of this is going to a regular zz gear set up. This is not going to increase speed at all, it will hinder it greatly.

Also, since the motors are going to fight each other, your battery life is not going to be very good at all.

To hook up 2 motors, they need to be on the same gear ratio as the drive axle and have as closely matched rpm ratings as possible.

If you're looking for torque, mount the orange gear on the regular transfer gear and hook up both motors with the same pinion to that one. If you're looking for speed, put a blue gear on both motors and mount them both on transfer gear directly (not via the smaller gear in the middle).

I have a zz that direct drives the axle gear and there is way more than enough power to do that. Lower gearing really isn't necessary for a car.

I'm sorry, but I don't think this is going to work.