"Oh my god" ... 166 central locking again
Well, I have had every door (apart from the driver's) fail at some time or another?
In my case, it has never been anything major like a faulty door lock or solenoid but just the Alfa "quirky" electrics. What I now do -every few months - is spray plenty of WD40 down the hole of the "pop-up" black plastic door pin and also down both sides of the door window black rubber seals in the general area of the door lock and allow it to trickle down. Leave the WD40 for a few minutes before doing anything. Next operate the door locks both manually and with the remote several times!
On my 166, one or more locks seem to temporarily fail after long periods of rain or dry weather

but seem to be easily corrected by the above method
I hope it works for you. (by the way, manually open the doors several times from both inside and outside the car)
It also sounds like the battery in your remote key is just low! (should work from about 40 metres especially if you touch the metal part of the key to your head while pressing the button

)