Write a system to choose and reserve points on a circle around the player. When the AI decides to attack the player they request an attack location from your Combat Circle and reserve it. When they die or get knocked out of some range they unreserve so a waiting or new AI can move to it.
This is the bare bones basic of how most beat em ups melee combat positioning works (God of War, Assassin’s Creed, Batman, etc)
You can try generate properly nav mesh volumes with higher cost around AI’s, that begin attack character I think, then non-attacking AI’s will be forced come round attacking AI.