Sorry for the delay in answering your questions. Your posts were not showing right away because you are a new member, and Admin holds the first few posts for review.
Your questions about having your girls spayed at the same time...I would do it that way. Get everyone taken care of in one day and then they can recuperate together.
Are they fighting mainly when they get excited, like seeing something at the window as you mentioned? Or are there also fights over toys, food, or whatever?