Use karma for the first one. U place despara in mid and a very strong archer on the left platform then use karma's skill. After u kill the first one , u place units in front of karma (to keep her alive) untill the next black ogres hit , then u activate karma's skill again and let her tank it again if u need it.
Edit : i'm jelly as fuck of your units. Congratz. That's a very nice team
Edit 2 : https://www.youtube.com/watch?v=wInoI0FdBmE do as this dude did