I only used this stroller as a single and so I can not compare it when used as a double but it can not be folded when in double mode with the seats attached. (strollerdiva.com)
Double mode mirrors playback to both speakers, whereas stereo separates them into left and right channels. (digitaltrends.com)
The full width of the stroller in double mode is 29 ″ which will easily get through a regular doorway. (momsstrollerreviews.com)