The door solenoid is definitely your problem and you need to change it to get the central locking to work properly. They are a bit of a pig to change and a new solenoid was around £85 last time I biught one.

It's a REALLY common problem. I only know of one person who's had a problem with fuse 63 but the good old internet makes out that's the more common fault. I've had 4 mk1 Focus's in both 3 and 5 four guise and I've had to change a front door solenoid on every single one.