What I don't understand is why MS keeps giving what are essentially confusing and overlapping choices. First understand that the only preferred rooms from which you can see Epcot are also boardwalk views. Thus, if they are saying Epcot view they must also be saying boardwalk view . There are rooms in the boardwalk area around the central courtyard (which are also the ones closest to the elevators) that do not have good views of Epcot like the rest of the boardwalk rooms. Nevertheless, the dual requests you made are essentially for the same thing, a boardwalk view, unless MS is misdesignating other rooms as having an Epcot view when they really do not.
Things to consider are distance to the elevator and whether you want a dedicated studio or a lock-off one. The lock-off studios are connected to one bedrooms, the dedicated studios are not attached to any other room and those can be quieter than the lockoffs because you won't hear the neighbors like you might through the inner doors of the lock-offs. The dedicated studios with a boardwalk view will be the ones closest to the elevators (and have only limited views of Epcot). The lock-offs will be those further from the elevators but have excellent views of Epcot. In other words you might ask for boardwalk view, close to elevator and that will likely get you a dedicated studio for the grandparents.