Are family members usually able to tell when a member of their family has some sort of mental health problem?

Possibly: Family members do have the advantages of having good access to the social history and family psychiatric history and these could lead to higher accuracy. However, their diagnostic capabilities are clouded by family discord and favoritism as well as conflicts of interest between the role of a family member and the need for accuracy in a diagnosis in addition to the lack of training and experience.

Not always: Some families tolerate very unusual behavior, or are themselves quite ill and dysfunctional. For instance, families in which there is active alcohol and/or substance abuse often have unhealthy communication problems as well. On the other hand, healthy families usually do notice behavioral changes in each other, but may not be able to diagnose the problem and need a physician's help.