Hi. Appreciate your concern for your brother. Yes, Irritability, avoiding socialization may be signs of depression. But not necessarily. They may indicate pre-occupation with some major stressors in life. The fact that he is not opening up with the family makes it slightly more tricky. You may try to coax him to meet a counselling psychologist. Alternately, approaching a good homoeopath for any other physical illness may also help. As in Homoeopathy, the entire physical, emotional and intellectual persona of the individual is assessed and medicine is prescribed.