Isn't it possible that during our adventure through the Ministry battle they will mix in some movie footage or use lifelike AA's of the trio dubbed with audio from the movie? Like we are on our own adventure with previously unseen action and new characters, but occasionally encounter things from the movie using original footage or audio? Also keep in mind Harry and Ron used polyjuice potion to assume the identity of older men to break into the Ministry. They could have hired these same actors instead of Dan and Rupert.