I don’t know of any studies on the subject, but anecdotal evidence suggests this: It doesn’t work, especially in the long run. Even valid methods for improving communication, mutual understanding and collaborative problem-solving can be much harder for psychologists to use in their personal lives.
Therapeutic relationships are very different from social ones. Therapists are not involved in clients’ day-to-day activities. They meet for the sole purpose of working on psychological issues. It’s agreed when and how they should meet. Roles and expectations are clear. Therapists are remunerated with money, not reciprocity. These ‘contracts’ help to make the psychological interventions effective.
In a family setting, interactions lose this structure and clarity. The fact that psychologists are direct participants in what’s going on means they have their own needs and agendas so they cannot maintain the same detached, independent perspective. They also have more significant roles such as mother, husband, son etc which supersede that of ‘psychologist’. The other difference is that family members usually know their relative far better than clients know their psychologist.
So the most likely thing to happen is that the psychologist’s efforts will be recognized and rebuffed – with some extra resentment and mistrust thrown in for the fact that they tried. Any attempts at manipulation, successful or not, will make people more guarded and apprehensive. They may even withdraw from interactions where they feel they will be ‘outsmarted’. Other family members may learn how to spot the tricks and eventually how to practice them.