|1) STOP YELLING AND HITTING YOUR DOGS!!!!!
2) Get a Different Vet Right Away!!
They are dogs, you are human, it is your responsibility to control yourself. If they were human infants, would you treat them like that? What you are doing is called Animal Cruelty. I know you don't mean to be cruel, you don't know any better, that's why I'm going to give you the opportunity to correct your behavior. Now ...
Chihuahuas bond very closely to one or two people, their entire universe revolves around 'their human' and their entire existence is devoted to the love, adoration and protection of their humans.
When you leave them alone, they panic, because they don't know if they will ever see you again, they feel abandoned. Remember, they are babies, they have no concept of time or distance, when they can't see you you don't exist, and that frightens them out of their tiny minds.
They're not doing it out of spite or to get back at you, they're doing it because they are Terrified! They are chewing to relieve anxiety, yelling only makes it worse because now they both long for and dread your return.
You must take control. By leaving them the run of the house, you are exposing them to a wide range of items with which to relieve their stress. It is your fault if things are getting chewed up, you are the one that left the items where the dogs could get at them.
Ideally this training would have started right away, before this pattern developed. You will now have to earn their trust, they're frightened of you because you yell and hit them seemingly for no reason. Unless you see them chewing and scold them right away, they don't know what they're being punished for. Like human infants, they live in a state of perpetual NOW, they don't remember that they chewed the shoe two hours ago, all they know is that you waved something in front of their nose and then you hit them.
You must start to train them that Mommy (or Daddy) Always Comes Back. When you have to leave the house, put them in a chihuahua proofed room (I used my bathroom with the tile floor) so there's nothing there for them to destroy. Put their food/water and their beds in the room, along with a few toys. Don't make a big deal about leaving, just say "Bye Bye" and close the door.
They should start sleeping in this 'safe' room right away. You may have to put up with crying for a few days, it's no different than teaching a human baby to sleep in its own crib. Don't reward them for crying by going to get them, wait until they stop and then praise them for being quiet. "Good puppy, quiet is good, go sleepy now". Do the same thing for brief periods in the evenings when you are home. They are in their room, but Mommy is still there and everything is OK.
This should be where they go whenever you have to leave. It's not ideal to do this before you have finished the desensitizing exercises below, but I'm going to assume that the reason they are left alone is because you have work or other commitments that do not allow you to take a week off of work. When you do have days that you can be home all day, begin the following :
Start slowly, put them in their room, calmly close the door, leave the house and wait 5 minutes. Come back in, open the door and praise them for being good. Then do this again and wait 10 minutes. Continue to do this for several days. Gradually extend the amount of time they are left alone. Eventually they should come to understand that Mommy Always Comes Back and stop being destructive, then you can slowly allow them access to other parts of the house while you are gone. Remember, it is your responsibility to remove forbidden items from their reach.
Because this has been going on for a while, you may need to give them something to reduce their anxiety. A good vet can assist you in this. With time they should come to trust you and be calm when you are gone, but most of the work will be on your part. They want to make you happy, they love you, they act out because they love you So Much It Hurts To Be Separated From You. They can learn to endure it, with lots of love from you.