Hi,
You only need 1 collider per hole
and you will have a trigger event on the enemy, the tag will know that there is a hole
when triggered you can do what you want, depending on your enemy
from your turtle sample, you only need a trigger event (with that tag) on your Red turtles
green turtles will continue and fall down.
if you would have a turtle on a hover board, you still use the same to hover over the hole.
If you want i can make a video to show you want i mean