first of all i suggest to use the distance expression for the distance control: distance(player.x player.y, enemy.x, enemy.y) < X
For your sounds you can use another random number before choosing a random sound. Give your enemy an instance variable.
Using an instance variable ensures that each enemy acts individually.
Then instead of choosing a sound, set the instance variable to choose(0, 1).
Create a sub-event:
If instance variable = 0 (or 1) -> play sound choose(a, b, c...)
Edit: To prevent the enemy from yelping again and again, you can give him another instance variable, add this to the condition and change it in an action.