Can they drink water with the mesh muzzles on? You might want to invest in some cage/basket or wire muzzles if you plan on keeping both dogs. This style of muzzle allows the dog to open it's mouth to pant and lap up water.
Here are some examples of the muzzles I'm talking about:
You want to make sure the dog can drink and pant when ever they want. Most pet stores don't carry these types of muzzles though so you might have to ask a trainers or shop around online. Alot of the bigger chain pet store might even be able to order you some.
If you only need to muzzle to keep them from chewing why not use an E-collar (cone collar)
If the dogs ever have a chance ,at all, of coming into contact with each other again, they should be muzzled at all times. It's not a happy way to live, but it's better then being chewed up.
You don't want them to get hurt again, or a person to get hurt while breaking up a fight. Especially if you have small children in the area or your own small children who might unknownly end up in the middle of the next fight.
Perhaps you should consider re-homing one of the dogs. I know nothing about the situation but from what I've heard this might be in the best interest of both of the dogs. It a hard choice to make but think of the quality of life of the dogs. You have to keep the dogs safety and your own in mind.
Dog aggression is a BIG issue that needs to be trained out of the dogs early as possible. You should see if you can find any place in the your area that offers training classes, some shelter and ASPCAs will offer free classes or greatly discounted classes.
I my self own a dog aggressive dog, who I have been working with for over a year and 1/2 to break that aggression. She is in a single dog home, but we still encounter other dogs so I've been working with her. It take a long time and alot of care. I wish you good luck.