Family therapy is useful in times of family crisis, or when a family needs support due to stress situations (illnesses affecting family members, childbirth or adoption, death of relatives etc.).

It is not obligatory for all family members to take part in this kind of therapy; on the contrary, this could lead to clashes and additional problems, so having previous counselling about the participating members is a necessity.
It is not always necessary nor recommended for all family members to take part in the sessions.