Hmmm this is a tough one. I'd hate to see either of the dogs harmed, emotionally or physically and I know you have a soft spot for both of them which is what is causing this dilemma for you in the first place.
First -- There is likely no way you are going to resolve this issue by Christmas. If there really is a plural on the "friends and relatives" that will be taking care of the pets while you are gone, please consider leaving one of the dogs with someone separate from the other dogs to ensure no one even has the chance of acting out.
Separation for safety is the first task that needs to be accomplished...even before you leave. Muzzling for long periods of time can be hard on a dog. Keeping them in separate rooms even should be much simpler on the dogs providing none of them are left alone for long periods of time. They all need your love and affection equally of course.
Two alpha females who have not "figured it out" after three fights is a scary situation but the older dog is going to have a much more difficult time finding a home. A behaviorist may be able to see something you are missing. Possibly it's a certain toy, bowl, location, action, or look that's causing the trouble and if you can pinpoint that then you may be able to resolve the problem rather quickly.
I don't have answers for you...but I do sympathize with your situation. I hope something works out no matter what you decide. The goal is the safety of you and each of the dogs. For the immediate situation..especially while you are away, please consider separating them completely.