Your little 9V batteries are used in a smoke alarm where the current is 0.5mA when waiting and is 20mA when beeping.
You measured 450mA when your motor is running. After half an hour the motor will get only 5V or 6V and run very slow.
You will probably see a brand new battery causing the motor to be slowing down.

With the Genie powered by 4.5V and the H-bridge powered by 9V, then if you use PNP transistors or P-channel Mosfets on top they never turn off because level-shifters are needed for them to turn off. The level-shifters can invert the signal to them instead of re-programming the Genie to do the inversion.

I will definitely do this tomorrow and will post my results. Will the top transistors turn off if I turn of the signal using the chip or will I need to create level shifters?

OK, here's a starter for 10. The FQP27P06 and IRLZ44N are available from CPC. They are both TO-220 cased devices so a little bulkier but won't get remotely warm. I've used your existing ZVN4306A as the level shifters for which they are perfect. This circuit will handle much larger motors and higher voltages so gives scope if you need to beef up the motors. I'm sure my AAC friends will have many comments

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Ooooooooo this looks pretty cool. I will make this as well and post my results also. Quick question on it can i assume it would be ok to program the microcontroller to create the pulse for the PWM's as well as triggering the enable pins?

 

Quick question on it can i assume it would be ok to program the microcontroller to create the pulse for the PWM's as well as triggering the enable pins?

Yes. Use two of the PWM outputs (analogWrite()) and two other GPIO pins (eg 8, 9, 10, 11 on an Arduino Uno). You'll probably find that the motor won't do much til you get to 30% or more on the PWM.

If you want to run the code by me before trying it, feel free...

One thought, with these motors it's probably not an issue but with freer running higher torque larger motors it's a good idea to brake first before changing direction else they try and tear themselves apart.