Some people look like their dogs. And many people act like their parents. This is a recurring theme in Ordinary People. The parents, not the dogs, that is. Seeing Conrad's grandparents—who are Beth's parents—doesn't provide us with any aha moments or epiphanies. But we can infer one thing from Conrad's interaction with them.
Conrad's grandmother likes to complain. She complains about Conrad's hair, his clothes, his behavior. Nothing is good enough for her. It's annoying during just one dinner with the old fogies, so can you imagine growing up with this woman as a mother? Perhaps this is where Beth's perfectionism comes from. Practice doesn't quite make perfect, but nagging your child into submission will certainly make them neurotic.