Need help detecting enemies

Im trying to create a dome shape arena that the player have to fight inside untill she deafeats all the enemies inside of it. How do i go about doing this. I manged to create a dome to enter but how do i know how many enemies are inside only, i was thinking of using get actor of all class but how do I do that but within a range only ?

make multi trace sphere inside dome, get everything was hit and filter by enemy class

Tks that helped alot ^^