Im currently making some enemy AI code for exactly that and will contribute it once Ive got it done to my liking with values that can be changed to create different enemy tactics. I hope to have this done sometime next month.

I tried explaining a simple method in the meantime but its actually not very simple at all

Basically it was to do with creating six cube entitys (passable/invisible) that follow the player but always at a set position surrounding the player.

If an enemy approaches assign one of the positions of these cubes (the nearest) to it and have the enemy move to it and not allow another enemy to take that position.

Enemies would have to be able to pass through eachother or otherwise they would get stuck in eachother trying to get to their position.

Also the player would trace to each cube to make sure they are in the same room or within the corridor the player is in and not in a wall. If in a wall, turn them off so enemies wont smack their heads into a wall trying to get to the position.

Hope that gives you some help, sorry no code.