Hi! I am having a similar problem as you. I have a neutered male/female duo and recently took in a female. The male is not accepting of her. A couple weeks ago, I made 2 nest boxes out of plastic storage containers. They are lined with fleece squares and they mount to the sides of the cages and are lined up with each other. The "back" of the nesting box, which is the side that is against the cage, is completely open. The 2 cages are placed right next to each other, and I placed vinyl mesh (like bonding pouch mesh) on the adjacent sides of the cage so that no one can reach through the bars. This way, everyone is essentially sleeping next to each other. They can see and smell each other through the vinyl mesh, but no one can reach and grab each other. So far, I haven't noticed much crabbing but I don't want to force things.
Have you tried cage swapping in addition to the pouch swapping?
I have heard of having them in separate bonding pouches during the day and the pouches being next to each other so they are close while they sleep but are unable to fight. I haven't really had success with this because my male isn't a fan of bonding pouches.
I have also heard that males tend to get aggressive when there are less females than males. Not sure if this is the case for you though as it sounds like they are only aggressive towards the female, not towards each other.
If you find something that works for you, please let me know, and best of luck to you!