So many movies intended for the big screen are having to forgo it these days, it seems odd when something as apt for home viewing as “Half Brothers” makes the COVID-defying move of opening on 1,200-plus American screens. Those looking for undemanding entertainment may give it a passing grade, but this formulaic, sometimes maudlin buddy comedy about reunited Mexican and Yankee half-siblings is not the sort of thing that cries for a public auditorium’s bigger scale or the collective viewing experience. Nor does writer-producer Eduardo Cisernos’ concept (its story co-credited to Ali LeRoy, the screenplay to Jason Shuman) add much to culture-clash politics beyond contrivance and reinforced stereotypes. It’s a slick film that’s forgettable at best, annoyingly broad and unfunny at worst.