The Coconut Connection — Cynthia Blair

When the Pratt twins' Christmas gift is a surprise trip to Hawaii, they expect a relaxing trip in paradise.  But Chris and Susan soon discover that a tiny island off Waikiki harbors a secret.  The clever, courageous girls can't resist solving the mystery, once again using their identical appearance to accomplish the impossible! #13 of the Pratt twins series. Young Adult Fiction by Cynthia Blair; originally published by Fawcett Juniper