It's pretty easy to make a basic follower. They need to have two packages: Stay and follow. One can be a basic wander package with a small radius (Or none), while the other is a follow PC package. The follow package should have a condition for a quest variable. That variable can be set through dialogue, so when you tell the guard to follow you, it changes the variable to thr follow option, then when spoken to again you can tell them to stop following you.
There's probably a tutorial out there that can phrase it better, though.
As for the rest of the AI, it's a fun effort to make the guards have schedules. Have them sleep for several hours, then eat for an hour, patrol for several hours, eat, then repeat the cycle. I'll go find the tutorial for that... Ah-hah! Here it is. Once you have that set up you can set it to specific hours of the day, then fill in other activities in the rest of the time.