You might have a combination of problems.
Litter mates may fight regardless of gender or sexual status.
Testosterone might be present in measurable amounts in the body up to 6 months after a neuter. Plus neutering is not some magic panacea that will correct non sexually dimorphic behaviour. And, recent research based on CBARQ shows more aggression in neutered dogs, not less.
Age one or so is when many dogs come into themselves and start to stand up and assert themselves.
Border Terrors are a feisty little dog and not for the faint of heart.
By hormone supplements you mean adding testosterone back? Depends how recent the neuter was whether you need that. I suggest you check out the Champdogs website, in the U.K. and ask about that there. That's the only place I've seen that discussed and folks there seem to be doing it for the male dog that is neutered and bullied by other dogs.
I don't suppose someone crossing BT with W, deliberately or not, can be considered a reputable breeder but have you asked the person you got them from? Lots of people do keep litter mates, especially as working dogs on a farm and there's another idea. Small as they are these dogs are high energy and need to work so are they getting enough exercise?
Good luck. The one thing I see that you can do yourself immediately is the exercise. I'd also get them into obedience classes, separate classes so they learn to focus on you as leader and not pay so much attention to each other.