RUNNING IN THE FAMILY by Michael Ondaatje (Penguin: $6.95) . A noted poet, novelist and film writer, Michael Ondaatje has compiled a series of brief sketches describing the antics of his dotty relatives in Ceylon during the '20s and '30s. Although both sides of his family had been prominent in Ceylonese society for generations, they all appear to have been as mad as hatters. Ondaatje describes his father as a gentle, if ineffectual man--until he went on one of his periodic binges, when he would stop trains by brandishing his Army pistols in the passenger cars, or by hiding naked in the tunnels. Near the end of her riches-to-rags life, his grandmother had to be barred from public parks because she insisted on picking the flowers and giving them away with the prodigal generosity she had displayed during her wealthy youth. Funny and oddly enchanting, Ondaatje's prose evokes a happier time in Ceylon, before ethnic strife shattered the island's tranquil existence.