Not so easy ^^
RayKi is right, if you want your npcs look at the player, when you're talking to them, you have to check and compare the position of your player and your npc. Depending on your game, the npc will change animation (4 directions, or 8) or make a rotation (so rotate toward position or set angle toward position). You have to implement a way to know when to trigger the effect and change the npc state.
Pseudo logic :
- when talk key pressed (or any other way)
- check and compare player's position and npcs position to get the nearest one
- pick it and make it change state and animation to start diaglogue
For the npc stay in an area, I assume you already have a behavior or them to wander (you talked about make them stop wandering). There are several ways to do this. You can simply set a zone with an invisible sprite stretched to the desired dimension. When sprite are overlapping that zone, they get wander position inside it, or don't move, if they aren't overlapping that zone, they tend to reach it. For performance reason, you can check overlapping every 0.1 or 0.2 seconds, and not every tick as it's not necessary or this.