‘Like her husband, Jackson Pollock, Lee Krasner was an Abstract Expressionist artist, and [the two of them both] influenced each other’s work.’ [the two of them both] is incorrect and should be replaced by [she and Pollock]. Is this simply a case of wordiness or is there something else going on? Thanks!

This is an issue of redundancy. “The two of them” and “both” aren’t both necessary.