WHEN THE FLT WAS APRX 15 MI WEST OF LANAI ON A CARGO FLT FROM HONOLULU TO HILO, HI, THE PLT OBSERVED THE FUEL GAUGES OSCILLATING ERRATICALLY TOWARD THE LOW SIDE. HE DIVERTED TOWARD LANAI TO REFUEL. HOWEVER, WHEN THE FLT WAS ABT 9 MI WESTOF LANAI, THE LEFT ENG FLAMED OUT. THE PLT FEATHERED THE LEFT ENG, BUT SHORTLY THEREAFTER (ABOUT 2 MI WEST OF LANAI), THE RIGHT ENG FLAMED OUT. WITH BOTH PROPS FEATHERED, HE ELECTED TO LAND ON AN UPWARD SLOPING ROAD. DURING THE LANDING ROLL, THE PLANE'S LEFT WING TIP STRUCK A SIGNPOST & A DIRT BANK WHICH CAUSED THE PLANE TO PIVOT FURTHER LEFT & NOSE INTO THE EMBANKMENT. NO FUEL OR FUEL LEAKAGE WAS FOUND DURING A POST-ACDNT EXAM. WHEN 1ST CHECKED, THE LEFT OUTBOARD FUEL GAUGE INDCD 70 TO 80 LBS OF FUEL REMAINING. LATER, BOTH LEFT FUEL GAUGES HAD ZERO READINGS. THE RGT OUTBOARD & INBOARD FUEL GAUGES INDCD 25 & 20 LBS, RESPECTIVELY.