A: Yes it can
A: Quiet Walls and Quiet Walls Commercial can be installed directly over existing drywall and covered with another layer of drywall. Quiet Walls Theater Residential is designed for this type of installation.
A: I am not sure - please note this product works best behind drywall because it will break down from UV.
A: That is probably a question for your landlord but probably not. The walls between the units is a fire wall which should go all the way to the roof. The wall will be the sound and fire barrier between the units. Your ceiling will have little to do with sound between the units maybe from rain hitting a metal roof. Besides all that the quiet wall membrane is very heavy and slippery to hang on a ceiling requiring several people to so.