I agree with Pat. IMO, the fact that you've had 4 peaceful years is a gift, I've only been able to rely on 2 years.
I would never depend on them getting along nicely, but sometimes convincing them that YOU are still alpha might help. Ways to do this:
Hold yummy treats in your hand, give a bite to the one that seems most in charge, insist the other wait. Then switch. Keep doing this until your hand is empty. When trouble starts, games over, no treats. Try to always end with the alpha.
Try walking them on a leash, maybe with your husband. I find 2 that are not best friends seem to find the different world so interesting, they sort of ignore each other. Doing it often enough will maybe help them to realize they don't always have to be hating the other.
When they are fed, do it in crates. Give the alpha hers first.
Hopefully the girls will decide that alpha is alpha. Like I said I'd NEVER trust them together, but maybe you all can get to the point that they aren't going to try and kill each other.
I've read, and experienced, that dogs are most at peace when who is alpha is known. they're not like kids, don't care if one got more, as long as they get some too. So, pick an alpha and treat her as such.
I have 2 that a few years ago hated each other, to the point of bloodshed if given the chance. Now, when one walks through the room that has the other in a crate, it seems to be more fun than hate to run up to the crate (guarded by an ex pen layer of protection) and then run along. Both girls do this. I envision someday actually being able to have them in a supervised room together, but we'll see.
(Their mothers absolutely wanted to kill each other. They both had totally different personalities and outlook on life, that they just couldn't get along.) These 2, it might be possible. I've been working on it for years and they are 12 and 14.