Will Penny (1967)

Will Penny, an aging cowpoke, takes a "line-rider" job on a vast cattle ranch requiring him to keep trespassers and squatters moving until they're off the property. Ironically, he discovers that the mountain cabin reserved for the line rider has been appropriated by Catherine Allen and her young son, Horace, whose guide has deserted them en route to Oregon to join Catherine's husband. Too soft-hearted and ashamed to kick mother and child out just as the bitter Rocky Mountains winter sets in, he agrees to share the cabin until the spring thaw. But it isn't just the snow that slowly thaws; lonely man and woman soon forget their considerable dissimilarities and start developing a deep, if awkward and unstated, love for each another. Beyond this, Horace finds in Will the father he's never known, and Will finds in Horace the son he's never known he's wanted. The trio's little refuge is then invaded by Bible-quoting preacher Quint and his murderous family of "rawhiders", who'd earlier nearly killed Will over an imagined insult, forcing Will to defend his own "family".

IMDb: https://www.imdb.com/title/tt0063811