Tracey Dewart faced a daunting task last summer: moving her 84-year-old mother, Aerielle, from her Manhattan apartment to an assisted living facility in Brooklyn. Her mother, who has Alzheimer’s, didn’t want to go, but there was little choice after she was found wandering near her home on the Upper East Side several times.

It was “physically and emotionally a horrible and overwhelming time,” said Ms. Dewart, 58. “It felt like there had been a death in the family as we had to sort through all of my parents’ belongings.”

And she was about to confront another ordeal — one that could serve as a cautionary tale for anyone who helps manage their parents’ money and, more broadly, anyone who does business with an investment broker.

To help pay for her mother’s care, Ms. Dewart relied on an investment account at J.P. Morgan Securities that her 89-year-old father, Gordon, opened at least eight years ago. The account was already paying expenses for Ms. Dewart’s father — who, after two strokes, was living in the residence that his wife was moving to — and for Ms. Dewart’s younger sister, who lives in a community for adults with developmental disabilities.