If you are the eldest son, your parents are afraid of losing one. What do you mean, husband and wife don't support their children and the family is not harmonious?
If a person is the eldest son, parents will worry about losing one, the relationship between husband and wife will be disharmonious, the children will be difficult to rely on, and the family will be uneasy. This sentence implies the importance and responsibility of the eldest son in the family, and his existence and role play an important role in the stability and harmony of the family.