Sounds like you got three weird, extra holes
I have a 180 w dual overflows.
Each overflow has a drain out and a return back in.
I might plug the three extraneous holes and set the overflows and returns properly.
Remember the overflow rate is dictated by the return pump at head height.
You need the overflows in the towers to be set up correctly with glued PVC
and proper bulkheads.
The returns can be set up any way you'd like with bulkheads and glued PVC
Keep it simple !!! Less bends the better.
Let me know if you need more.