Hello,
I was wondering, if is there any way to tell an NPC what EXACTLY to do?
I see, that to change their leveling scheme, you'll need an unofficial patch, but is it possible to, for example tell someone to pick a lock, or such?
If not, why are there skills as lockpicking, or persuasion keep increasing at some characters?

If you attempt to pick a lock and one of your party is better at it than you they will say "I'll do that for you" and take over if you give them a bit of time. Other skills are less useful really. I've almost never attempted to rely on follower skills.