I know that twins make you crazy form personal experience, but a twin engine VTOL!! Got to love it!!
I cannot add to the above ideas beyond one more input. As stated above, controlling two engines will be more than a hand full. If you will go to a post I did concerning hovering with twins, I did do some experiments with the installation of a twin input and output gyro for one of my twins with a single tail, and was reasonably happy with the results. i would also voice that I am not sure the engines will or can react fast enough for this project, but I would stronly suggest discussion with the Helicopter guys about additional gyros for control.
Good Luck,
Send Pictures!!!!