I know you mentioned BC is booked and you are probably not going to be there, BUT I was just in a studio there during Spring Break. It is small with 4 people. I have 2 kids that are little (4 and 8) and it was tight with us. None of us are particularly large either. Just want to put that out there. I believe BW is similar square footage to BC.
However, if you think you will be 3 days total between HS and Epcot, that location cannot be understated. We LOVE it there. Either hotel. You can walk or boat to HS or Epcot and the Skyliner is fun to just tour around other places.
I would look into the square footage/sleeping surfaces of the studios and then see how it compares with 1-bedroom and cost. You may find it worth it to go to a less expensive option but more space.