**_A group of youths shipwrecked on an ominous isle in the Great Lakes_** In northern Lake Michigan two conflicting brothers take their girlfriends and sister on a trip in their father’s yacht to St. Martin Island, but wind up in the fog on “Dog Island.” The mysterious isle is the home of a reclusive lumber baroness and guarded by a pack of German shepherds. Will they make it out alive? “Humongous” (1982) is an artistic horror flick with slasher elements obviously influenced by Joe D’Amato’s “Anthropophagus” from a couple of years earlier, along with bits from “The Shuttered Room” (1967), “A…