ah, i also translated 'Can we open the door'...note to self....look at punctuation :)
Sounds OK to me. (I only see the fast audio button, translation from Italian to English)
Depends on the punctuation I guess. If this sentence was as an audio question then it's hard to tell if it is a question or not, but as a written question then "Possiamo aprire la porta." would only be a statement.
Most of the recordings don't have the last vowel, as if they stop recording before she finishes the word!
I'm thinking not, the infinitive is being used as an imperative here. Aperta is the past participle. It would be like saying "don't opened the door"