Binuclear families differ from joint-custody families in that

The correct answer is "not all binuclear families have joint custody and in the binuclear family, children are always part of two or more households".
A binuclear family is formed after a divorce of the parents; in this extended familial organisation, both the parents are highly involved in the upbringing of the children. Sometimes, children of binuclear families are part of two or more households, as their parents may remarry and form new families with their subsequent partners. In joint-custody families, the divorce was finalised with both parents sharing custody of their children.