The answer to the first question is very interesting; it vaguely ties in with the idea that the hero and the protagonist are not necessarily the same person. It seems to me that Mildmay (gross generalisation alert!) tends to act more heroic (and is certainly easier to sympathise with) but Felix remains the protagonist.

To some extent it depends on whose agenda is being serviced by the story. While Mildmay goes off and does his own thing at various points, the story still primarily revolves around Felix's actions, issues and needs (a trivial comparison: in the final season of Farscape D'Argo is voted as captain of Moya, but it is still John's agenda that drives the plot).