It Happened on Fifth Avenue (1947)

Every winter, Michael J. O'Connor, the second richest man in the world, vacates his 5th Avenue mansion for his winter home in warmer climes. Every winter, Aloysius T. McKeever, a homeless man, moves into the vacated mansion. This particular winter, McKeever meets Jim Bullock, an army veteran who has recently been evicted from his apartment and offers to share the mansion with him. It's not long before the mansion has a few more guests, including two of Jim's army buddies and their wives and children; runaway heiress Trudy Connor; her mother, and even Michael J. O'Connor, himself.