The best chance of getting a room that will see the higher level fireworks from Illuminations will occur if you manage to reserve a Preferred view - Boardwalk view. You'll need to call day by day when MS first opens to be sure of getting the Boardwalk view for your entire stay. (There aren't a lot of 2 bedroom units that have a Boardwalk view, but if you get one, you will be able to see the fireworks and the room category - Boardwalk view, is now guaranteed).
Your other choice is to request a standard view (less points) and you will have to call day by day to get that, too. However, not all of the standard view rooms have a view of the fireworks. You'll need to request an upper floor room that is across from the bus stop and hope that you get it. Quite a few of the standard view rooms overlook the entrance driveway and the fireworks view form those rooms is blocked by the BWI and the convention center.
Most of the rooms that have a fireworks view are not close to the elevators, so keep that in mind. There are several stairways scattered throughout the resort, but sometimes those with little ones along cannot use them (strollers). For some, the extra walking to the elevators (and IMHO, it isn't all that bad) is worth the fireworks view.
Good luck!