[Christ]

rear window problems are probably the motors, they go bad over time..

Yes, you should clean inside your doors, 20 years is a long ass time for stuff to get into your doors and mess everything electrical up.

The locks, either all four solenoids went bad randomly (highly unlikely) or you just need to check the wiring and check/replace the switch/fuse/relay.

You can check the master switch by removing the switch from the wire clip and jumpering the wires, there are three, lock (+)/unlock (+) and ground (-)

Same with all the window switches, and you can add a voltmeter to them to make sure that they're working with the right voltage.

Check the fuses for all too, since you're going to be doing stuff with electrical, it never hurts.