Families rarely fall out over the thing they are currently arguing about. They fall out over roles allocated decades ago that nobody has been allowed to put down.
You can be a competent adult everywhere else and still become the fourteen-year-old version of yourself within ten minutes of walking into your parents' house. Family patterns are old, well-practised, and mostly invisible to the people inside them.
What people bring
Adult children who have stopped speaking to a parent. Parents who cannot understand why. In-laws, and the partner caught between two households. Caring for someone elderly and the resentment nobody says out loud. Estrangement, and whether to attempt contact again.
How family therapy works
Sometimes everyone is in the room, sometimes only the person who came. Both work. A pattern involving five people can shift because one of them stops playing their part in it.
Nobody is required to attend
You cannot make a relative come to therapy, and you do not need to. Coming alone to work out how you want to handle a family is a complete piece of work in itself.