you basically are balancing the plane on 2 columns of air in a hover... without some form of correction available a crash is inevitable... be it from a crosswind or a momentary glitch in the speed of both motors...
A Harrier has 4 nozzles, it has balance in roll and pitch inherent, but it needs a tail mounted "puffer box" to control yaw. the harrier has alot of anhedral in the wing and tail to help "dam up" the air underneath. you can see how it was exaggerated in the difference between the underside of an AV8A vs. an AV8B.
A JSF (F-35B - U.S. Marine variant) has motors like you are planning, I believe yaw is controlled by the articulated rear nozzle, as most of the lift comes from the front fan in a hover. leaving the need for available roll correction via the puffer vanes under the wing.

without these, you are in for a gamble at liftoff, either it goes straight up or it will drop a wing and flip over. unlike a 3d plane, c-grain is right on the money pointing out that your control surfaces have no effect during hover.
your setup would most likely emulate the JSF, therefore you will probably need a roll puffer system, hooked up to a gyro so you don't have to constantly balance it on liftoff and during the most critical phase of the flight... the transition to forward flight. this is where a design flaw will result in a full throttle nosedive... perhaps a delay in the pivot so the front stays pointed down while the rear transitions will help counteract the tendency to drop the nose (again, no control surface help until forward airspeed can be built up).

If you think it will be fine as is, build it and see... I'm all for experimentation :-) Do some google research and make sure you are familiar with what happens on the big planes during hover and transition. one really cool application for your plan as is would be short takeoff (the famous harrier "jump" that is done by leaving the back nozzles facing rearward and turning the front nozzles 45 degrees down)

I'm going to attempt a JSF F-35B after I am done with my current project (X-02 Wyvern from the Playstation2's Ace Combat '04 and '05 games) that is a testbed for a simple variable exhaust nozzle that I have been tweaking and developing for a few weeks now.

when you get it going, post a vid... hover with transition would be too cool!

good luck!