Servo Driven Through Custom Library Not working Properly
In C++, when an object is declared as a member of another object, the constructor method of the inner object must be called explicity (see constructors and member initializer lists).

In your code, properties of Servo type can be constructed within the header of the MotorControl constructor:

MotorControl::MotorControl(int north, int south, int west, int east)             
    : _north(), _south(), _west(), _east()                                       
{                                                                                
  _north.attach(north);                                                          
  _south.attach(south);                                                          
  _west.attach(west);                                                            
  _east.attach(east);                                                            
  _northVal = 0;                                                                 
  _southVal = 0;                                                                 
  _westVal = 0;                                                                  
  _eastVal = 0;                                                                  
}