This modest, melancholic road-movie drama concerns two brothers (Adam Rothenberg and Ethan Peck) who travel from New Mexico to Tennessee in search of their violent father. Why? Because Peck’s character has developed leukemia and needs a bone marrow transplant. Tennessee veers dangerously ?close to made-for-TV territory. But you utterly believe the bond between the siblings, and Rothenberg excels in his role of a protective older bro who also happens to be a haunted binge drinker. Mariah Carey is perfectly fine playing a waitress who dreams of becoming, yes, a ?singer — even if the superstar’s presence in such a small venture seems jarring. B?