as far as i know, B777 and A330 have 3 independent hyd system to power up the flight control surface, so if you both engine EDP failed, you should have center hyd system, with it, you still able to move the control surface, when both engine electrical pump failed, you will have APU to power up the aircraft electrical system, and center hyd, if you failed ur APU, you have RAT (Ram Air Turbine), which power up the aircraft and run the center electrical pump. and if RAT also failed... GOOD LUCK
. besides, i think when the pilot encounter 2 engine EDP failed, they will land at the nearest airport.
as for B747, we have 4 independent hyd system from 4 diff engine... to have them all fail, possibility quite low
