I don’t know what to do. I’m not sure if I’m right or wrong, and I need advice on the best approach. Almost 20 years ago, my parents also were able to save enough money for a down payment on a house.

My parents are downsizing. They are retired with enough savings to live well, but not enough to afford the new place. I can help—and I want to—but I want to make sure we avoid any pitfalls. I work ...