Krupa,
I'm sure that it's possible to control motors in the way as you describe but it's not an easy task and I don't think that it's a good idea to use stepper motors in an application that requires dynamic load and velocity changes. This type of application should be realized with servo motors as they can compensate for load changes which is not possible with steppers.
In general you will have to implement a kind of intelligent electronic gearing with a flexible master/slave architecture. In fact this task would be much easier with a tool like the
NI SoftMotion development module and it might be a major development task to do everything from the scratch by your own.
Jochen