Most young adults don’t expect to support their aging parents. Here’s what happened when four people had to.

Five years ago, Sian-Pierre Regis, then 35, welcomed new roommates to his Manhattan apartment: his mother, Rebecca Danigelis, 78, and his partner, Sam Moll, 30, whom he had been dating for two years. “It sounds like a sitcom — two gay men and a mom in a cramped New York rental,” Mr. Regis said. “It felt like this quirky experiment.”

They made the most of their tight quarters, constructing gingerbread houses together at Christmas and sharing “highs and lows” every Friday at the dinner table. But for Ms. Danigelis, encountering her son’s dirty dishes in the sink and sleeping in a windowless spare room was not exactly how she had envisioned her golden years.

Instead, the arrangement was born of necessity after she was laid off from her longtime job as a hotel housekeeper in