.......Your problem with the doors unlocking themselves is caused by the main lock relay in the DS door, its almost right under the lock and window switch console panel. These things seem to get sensitive to vibrations with age. If you knock hard it will activate. What happens when you use the power locks is the vibration from the locks be snapped shut or open in the door triggers the relay to activate. In some cases mine would do this several times before it would stop, as each time it activates it causes another vibration. Slamming the door would often activate it too, which can put you in all sorts of awkard positions. Keep a spare key in your wallet till you get it fixed. You should just need to replace that relay and all should be good. Finding one at a junkyard can be hit and miss as it is a common problem....
