THE FOUR OF US by Elizabeth Swados (Farrar, Straus & Giroux: $19.95; 223 pp.) This frightening memoir of writer/musician Swados’ childhood--with a schizophrenic brother, a mother who committed suicide and an ambitious, if overwhelmed father--has been excerpted as the cover piece of the New York Times magazine, and the selection, about Lincoln Swados’ life as a homeless denizen of Manhattan’s streets, is the most powerful material in the book. Swados was, for years, in her older brother’s thrall, both as a child, when his erratic brilliance drew her to him, and as she became a young adult, more aware of his increasing incompetence, often a victim of his stinging rages. One can only grieve for him, as he makes an extended descent into his private hell, and wonder how many others there are like him, caught between legislation to curtail the warehousing of people with mental problems, and the inability of our society to finance alternative shelters for them. The rest of the book (it is divided into four essays, reflecting each family member’s story) is, sadly, not as powerful. Swados’ writing seems to lack discipline, perhaps because the subject so consumes her; it is too often repetitive and flat, as though she had to recite certain events to be able to leave them behind.