Disney musicals from the ’50s and ’60s have a push-pull effect on many folks who grew up loving the stuff, then felt a need to distance themselves from it as young adults, only to rediscover the poignancy, sophistication, and melancholy of the music once again as adults. That layered, lingering power is due to the genius of brothers Robert and Richard Sherman, the only songwriters ever hired as Disney staff. The duo provided song scores for such classics as Mary Poppins, The Jungle Book, The Parent Trap, and Bedknobs and Broomsticks. But anyone expecting a saccharine-mapped trip down memory lane from this engrossing documentary, directed by cousins Gregory and Jeff Sherman, sons of Robert and Richard, is in for a bittersweet, heartbreaking surprise. Crammed with clips from classic films, insightful observations from assorted talking heads, and lots of family photos and home-movie snippets, Boys is first-rate cinema archaeology. What pushes it beyond that is the brutal honesty with which the sibling rivalry between the elder Shermans is depicted; theirs is a palpable mixture of love and disdain that led to the men not socializing with each other for more than 40 years, even as they worked together. You leave the film knowing that something of their music’s powerful undertow lies in the dark currents of their own relationship.