That dynamic is on display in “Still Alice”: The daughter in law school is married and has twins after struggling to conceive; the son is in medical school; the daughter acting in Los Angeles keeps her distance from both and seems to get along best with her father.

Of course, that siblings fight and harbor grudges from childhood is news to no one. But those adult children also don’t always respect their parents’ wishes. Consider when a person with Alzheimer’s wants to have a say in when he or she dies.

Ms. Moore’s character makes a video instructing her future debilitated self on how to take pills hidden in her drawer to commit suicide. The carefully detailed plan is the product of a lucid mind, something she no longer possesses when she later finds the video. Her effort fails when she is interrupted and forgets what she was doing.

William Zabel, a leading trusts and estates lawyer and a founding partner of the law firm Schulte Roth & Zabel, said it was difficult for people in the United States to chose dignified death on their terms. One of his clients wanted him to be with her when she took her own life at the Carlyle Hotel in Manhattan, he said. But doing so would have led to his disbarment.

But after the request, a lawyer at his firm put together a 21-page memo on right-to-die laws around the world. It is a difficult subject, and not just because of the moral issues. There are the logistics beyond the actual act. How, for example, would someone with Alzheimer’s get to a country that allows assisted suicide when he or she has only moments of lucidity, or find a doctor in the United States who might administer a strong dose of morphine?

His firm’s memo includes a “dementia provision,” where people can elect that a list of life-sustaining treatments be withheld and ask that their wishes regarding the end of their lives be upheld. It’s a strongly worded statement, but Mr. Zabel said it might not hold up in court, particularly in states like New York where withholding food and water from a person is illegal.

“In one case, I filmed the decedent about why he wanted to die in a dignified way,” Mr. Zabel said. “Just writing a letter is not the same as seeing it on film, particularly where there are family members who particularly religious and particularly not. You get into this moral quandary of assisted suicide versus dignified death.”