Great Pyrenees

We own 4 Pry 2 males and 2 females, and 35 acres to run and protect. Just in the last month our 6yr female got sick and severe infection and had to be spade, last week. The newest female to our home is a 8yr resue,that is breed and due Oct. 17th, she was being mean to the other female, I thought just trying to establish the Alpha order.
The 6yr female would lay under our deck and growel if any of the other dogs came by...Today it all came to a head! While my husband was petting the 6yr the other female came up as he was walking away, the fighting broke out, and was not controlable. For everyones safety I have the 8yr female in a confind area for now. Just really at a loss at what to do, and how to solve this issue.

I have heard that in a pack of dogs, which I assume they think of each other as that since you have four of them, that if there is a sick one in the pack, usually the other dogs will try and eliminate the sick dog because in their mind, being pack animals and instinctual, a sick dog will weaken their pack. Maybe that is why your dog is fighting the other one so frequently. It's they're way of ensuring the packs survival by eliminating any weak ones and ensuring their place in the pack as alpha.