Over the last few years, Linda Barton watched as her mom and stepdad progressively shifted from active 80-year-olds to, in her words, “children.” Her mom with dementia became unable to take care of herself, while her stepfather, whose health has also declined, “acts like he’s 6 years old.”

The commute to see them, which was an hour each way from work, wore her down, and she didn’t want them to move in with her because of space constraints. She did the next best thing: move them into her yard.

Barton, 55, and her husband bought a tiny home for $37,000 in their part of Texas, outside Houston. After months of installing a septic system, an…