In Half-Life 2 (and other Source games) they use a system called Choreography, which is basically a script that will tell the AI to do certain things in a certain order.
For example: You could have 1 action that tells the AI to walk to a certain position, then tells them to play their voice lines and maybe play a animation at the same time.
So basically what you need to do is make a system for directing the AI to do specific actions at specific times. You may be able to use the UE Sequencer to call functions on the AI’s blueprint to, for example, tell them to move to a specific position.