What is wrong with my central locking on my Vauxhall Vectra 2.5 V6?

I have a problem with the central locking system. First, the front passenger door stopped unlocking about 2-3 months ago. It stays locked when you press the unlock pad on the key and even if you manually pull the button up it is still locked. Then the rear nearside door stopped locking and unlocking with the key pad, but you could pull it up manually and the door would open. Then yesterday when I locked the doors with the key, the front passenger door suddenly unlocked and the door actually opened (even though the alarm went off as the car was in locked mode, even though this door had unlocked!) As I have not been able to unlock or even open this door for some months, I have left it unlocked, so at least a garage can open the door to get to the inside of the door panel, as they said it would be an extra hours labour just to get the door open, which now it IS open they will not have to charge this. Also the petrol cap, which I believe is on the samw system as the door locks will now not unlock! My partner has looked inside the box on the drivers side footwell where the central locking and alarm control unit is and all wiring seemed ok. He has also taken off the front nearside passenger door panel and looked at the wiring going to the motor and it seems ok. Anyone have any ideas?