If you want the deadlocks on but the buttons on the key won't work at the moment, put the key in the lock and turn it once to lock the doors and a second time to put on the deadlocks. If the sound is what you expect then that would seem to prove that the key isn't functioning properly. HTH
Are you sure that the same (uncorrected) electrical fault hasn't blown the fuse again? Has the a "mmh" sound stopped?
The handbook says in the event of an electrical failure the front doors can still be opened with the key. The manual suggests that the key turn direction is reversed for opposite sides of the car.
If the childproof locks are on you will not be able to open the rear doors from the inside. If the fuse for the locks have failed again then you will not be able to open them from the outside. Turning off the childproof locks requires the key in the hole in the lock - only accessible with the doors open.
If the fuse has gone again and you replace it try opening _all_try doors and closing them again before attempting the dead lock position in case the problem is something simple as incorrectly aligned lock mechanism due a door that isn't fully closed thus causing the lock motors to stall, taking more current, and blowing the fuse
Get two fuses in case you inadvertently dead lock the doors while they are still open and the replacement fuse blows again leaving one or more doors in the locked state :(
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