If multiple users are assigned as authors to a question, is it possible to get reporting insights on which user actually completed the question?
Yes, under Project Activities - Q&A - Activity there will be a "performed by" column.
Something I always recommend is to generate a Project Report every time you complete a project in RFPIO.
This will give you a high-level overview of all the actions that were taken in the project from creation to completion. It's an excellent way to not only track activity, but also to see where you can streamline or enhance your overall processes.