by BROOKE HAYWARD 325 pages. Knopf. $10.
Count no man happy, said the Greeks, until he is dead. Or a family, Brooke Hayward adds, in this intense, absorbing tale of her own. On Daughter Brooke's account sheet, the story of the Haywards is not so much tragic as it is sad. They were not visited by terrible events like poverty, disease, or accident: they invited unhappiness, as casually and as carelessly as they might invite a tiresome guest to a garden party; eventually they were seduced by its dark and terrible charm.