But the AI has guns so I want them to look at the player position
If you know the player position in global coordinates (and you say you do!), then you can use the
look_at-function for that. Check out the documentation.
I also want to make a gun shooting system how do I do that?
There are a couple of plugins for that like this and this. If you want to implement a hit-scan weapon (i.e. a weapon that doesn't actually fire a projectile) I'd recommend this.
shoot at them as well as follow them, how do I do that?
Take a look at this tutorial on homing missiles. You might find his series on implementing a tank battle game helpful as well, especially parts 3, 4 and 5.