QMy older sister, though trained as a pediatrician, has turned out to be a disastrous mother.

And yet she thinks she’s doing a wonderful job, even though her son, who’s nearly 6, is a bad-tempered child who rules their roost, throws tantrums and curses at us when we visit, telling us to go home. He also eats mostly processed, sugary treats even before a meal, spends at least eight unsupervised hours a day on the computer — and still wears diapers.

My mother took care of him a few weeks ago when my sister was in the hospital having twins, and he told her to “go away” and yelled “I hate you” at her every day, even while expecting her to carry him around, do his bidding and change his soiled diapers. Once my sister came home, she wouldn’t let our mother correct her son, even mildly. She said that she had to soothe the boy as she did, which meant, “Give him whatever he wants.”

He also has very few friends because my sister thinks other children are dirty and bad and also because she has been isolating him for years. On her only visit to my house, she quickly assured him that they’d leave soon and return to Daddy, even though he was enjoying himself, was happy to see his cousin and didn’t seem to care when he went home.

He has never been in a play group or gone to preschool, kindergarten or story hour at the library. My sister now plans to home-school him, but she hasn’t taught him much. He barely speaks English and speaks even less of his father’s language.

I think my sister has psychological problems and is turning her son into an emotional cripple. Now we’re afraid she’ll do the same thing to the twins, but we feel helpless because she and her family live in another city, because her husband — a much younger man from another country — defers to her about the children, and because she shuts out anyone who criticizes her, however gently.

She might take some guidance from our father, but what can the rest of us do?

ASince your sister will neither seek help nor accept it, you can only hope that some surprising life event will make her change — and it might, because life is never static. Just when you think it can’t get any worse, it suddenly gets better. And when it has begun to bore you silly, it improves in some surprising way.

Your brother-in-law may go out for a walk and just keep walking. Or your sister may walk off the set herself or have a breakdown or go back to work, rather than stay home with three pampered children. Whatever happens, look for therapy in their future, especially for your nephew. The super-attentive parent always makes her child feel angry and inept.

Whatever the situation, stay connected with your sister, not to give her advice — which she won’t take — but to be closer to her children. They’re going to need you one day.

Ask your dad to take the lead, since your sister pays more attention to him than anyone else, and to use the computer to connect with the boy, since he is on it so much. Perhaps your dad could start a Grandpa’s Blog, featuring short and funny neighborhood news flashes, spliced with Garfield cartoons and family pictures. He could also set up a regular Skype date with all of his grandchildren so this child, in particular, could hear more language. Even though he’s growing up in a bilingual household, he should learn to speak one language well so he can handle the syntax in all other languages.

Skype visits may also help your nephew relate to you and his grandparents better, although he’ll probably be as rude as ever. Don’t take it personally. Children and adults attack others for the things that they most dislike in themselves, and the deeper their dislike, the stronger their attacks will be.

Instead of paying attention to these rants, your mom could type up some recipes for your sister, in hopes that she’ll serve better food, and you could give her what may be the 10 best books ever written on child development, starting with “Your One-Year-Old” and ending with “Your Ten to Fourteen-Year-Old” (Dell, $14-$15).

Like most good parenting books, this series is based on the longitudinal studies that the Gesell Institute of Human Development has been doing on children since 1924, but these 10 books are better because they were all written by Louise Bates Ames, one of the Gesell founders; three of them were co-authored by Frances L. Ilg, another Gesell founder; and four of them were co-authored by Ames’s granddaughter, Carol Chase Haber. Their thoughtful, positive descriptions of children, age by age, may help your sister understand her own children better.

Questions? Send them to advice@margueritekelly.com .