I agree with the opinion that 2 girls that hate each other will make your problems. No amount of training will help.
I would better separate them. Indeed to care a dog and train the dog is a difficult work, I was always interested in how to behave properly with an animal and educate him. Here are some useful articles according to different situations and right attitude with your pet https://inspiredogs.com/how-to-know-if-your-dog-has-bonded-with-you-and-trusts-you/. Indeed, if he suffers from different feelings, he must be heard and to help him is the direct responsibility of the owner.
