I am looking for books *for* kids about gentle discipline, conflict resolution, working stuff out without fighting etc. I'm thinking picture books, but older audience than "hands are not for hitting et al."
Among the books in that list that look like what you are looking for is Elizabeth Crary's CHILDREN'S PROBLEM-SOLVING SERIES with the titles of: I Want It; I Want to Play; Mommy, Don't Go; My Name Is not Dummy; and I'm Lost; I Can't Wait. Elizabeth Crary also has a series called DEALING WITH FEELINGS including the titles: I'm Mad; I'm Scared; I'm Proud; I'm Excited; I'm Frustrated; I'm Furious
They aren't designed to be didactic, but the Charlie and Lola series by Lauren Child is full of great examples of a younger/older sibling pair getting along and solving conflicts in creative ways without fighting. Plus, the books are charming and GORGEOUS to look at.