No, not always. My T is a family therapist and he sees members of families in different groupings--whatever is needed. (I have seen him as part of 3 different groupings.) My daughter and I went to see a different family therapist--just the two of us--for family therapy. Since the relationship between the two of us was the main issue, it wouldn't really have helped us with that particular problem to have other family members present. Both of these Ts said that they would welcome other members of the family into the sessions. My T has even said he would welcome my mother.