Hello, I was wondering if it was possible for 2 people to work on an Experience Design project together. If this isn't possible perhaps, you could provide some tips so that 2 people can work in tandem on a project.
Second question: Is there a simple intuitive way to convert existing Desktop artboards into Mobile artboards without going through reformatting issues
Not yet, though we did share a vision about collaboration: Adobe MAX 2016. Day 1 Keynote (Chapter 3) | Adobe Creative Cloud - YouTube
Regarding the second one, I'm going to just say that designing for mobile and desktop are significantly different enough that you will definitely want to modify your design going from one to the other. If you're interested in smaller changes, you might want to upvote adaptive layout in UserVoice: Responsive artboards / adaptive layout constraints for resizing – Adobe XD Feedback : Feature Requests & Bugs
Hope that helps!