Introducing a puppy to two aggressive dogs?

Question
About a year and a half ago we adopted a Pomeranian/silky terrier puppy (Katie) into our home. At the time we had a pitbull mix (Brandy). Brandy and Katie got along great. But a year later, Brandy passed away from cancer. A month after we accidentally found a dog online who needed rescuing and was close to death, a 5 month old puppy named Eli. He's a Plott hound/pitbull mix. We decided to rescue him, hoping he'd keep our little Katie company. They got along great too.

A few days ago my family and I met a sheltie puppy who we really love and are wanting to adopt, but we are worried about our current dogs.

Both of our dogs have a serious aggression towards other dogs. They are extremely territorial too. About three months ago Eli attacked our neighbors 1 year old bulldog. The dog had 17 piercings altogether, 9 in his neck. They were all deep, his muscles were torn, etc. He did, luckily, survive.

Because of that accident I'm afraid that Eli and Katie are just going to attack and possibly kill the sheltie puppy if we get him.

Is there any way to introduce the dogs, without it getting dangerous? Eli is now 60 lbs and because of his breed, he doesn't stop until his opponent is dead. He only quit last time because five people were hitting him and prying his jaws open.

What can I do?!?! How do you introduce a puppy to two aggressive dogs?
(They are never aggressive once they know the dog, but because they are so protective of us and the house, they tend to get out of hand. They are good dogs, they just need to learn how to get along with others!)

Answer
There is absolutely no way anyone can advise you in this situation without evaluating both your dogs, but it sounds to me as if you already have the answer.  Introducing a puppy into a situation which might very well result in its death is unconscionable.