With the loss of thrust on both engines you'd be initially on the STBY power system powered by the battery. Therefore you'll have a nice 'AUTO FAIL' light illuminated and you'll be on your own in MANUAL mode.
Best thing is to get the APU running if available and put it on line. Then the pressurization will be controlled automatically. But remember no engines, no duct pressure! So descent to 17,000 close the isolation valve and put the LEFT PACK on the APU.
If the cabin alt horn goes off
MASK on then.
With both engines flamed out, you'll be busy initially trying to restart them. But remember, don't get sucked into trying to restart two dead motors, a la US Airways, if they don't relight, consider should be given to spending your limited time on preparing for a ditching....and there's a whole new checklist for that!
MK