(I've heard that married couples do that every now and again...)

I think they work well as a team. There is even a version of Max with a "Tomb Raider" style of outfit.

In my version of the backstory, Action Man was one of Max's instructors after he got nanobotized, particularly in mountaineering & parkour. Max, being AM's star pupil, drew the attention of his younger sister. She was not only attracted to him, but jealous of his ability, as well. This aroused a sense of competition in her. In her rivalry with him, they eventually got closer, gaining mutual respect and learned to anticipate each other's ways.