Introducing a new cat to your old cat

Hi all, newbie here...

Well, I have 2 Cats..1 I have had for 10years and another that I have had for almost 2. Both female. Starting last year, there was a stray male (Adult) that started hanging around the house, very good Cat and loving. My youngest (Mona) would interact with the male (KittyBoy) through the large picture window and the screen door on the porch with little to no fuss. the older female (Cybil) acted like she could careless about KittyBoy and couldnt be bothered with him.

As an animal lover I decided to take Kittyboy to the vet for neutering, not that he was spraying on or near the house but it was the right thing to do to keep the animal population down. After that he remained outside free to do as he pleases and go where ever he wants. We became attached to Kittyboy and beinging an animal activist i feared for him...be it snatched up and sold to a lab or the victem of animal cruelty.

So a few months later we took him back to the vet for de-Clawing so we could bring him into our home, it would be far to Mona and Cybil if he kept his claws. he stayed on the enclosed porch for almost 2 weeks recovering where he did NO damage to anything. He cried out for attention more then anything else. a few times we out Mona and Cybil in the basement so KittyBoy could roam the house and get some scent goin-on. Even though the girls new him because they could smell him on our clothes even before we decided to bring him in.

As of 4 days ago he is in the house and the girls are rather pissed. I expected this after I introduced Mona to Cybil. Mona would chace Cybil around the house and would want to play, but Mona never hissed or anything at Cybil, just wanted to play.

With KittyBoy it seems a little more evasive, I have been working with them. having them eat together (Cybil growling in her bowl and Mona on edge) but making sure the girls get just as much if not more attention. My lover told me tonight that "it sounded like Mona was being killed by KittyBoy", the scuffle was rather concerning. Tailes were flaired up as if they were dooking it out.

Would KittyBoy hurt Mona or Cybil?
Is it to late to try another tactic of introduction?
Will this matter of Terratorialism pass? and how long?
Is it just to late and we should just ride it out as it is?

I guess I am just worried about Cybil and Mona, I dont want KittyBoy to hurt them.

Were the cats just yelling at each other or were they actively fighting? If they weren't fighting, I wouldn't worry about it. You need to expect some hisses, swats, and growls as they try to figure out their new relationships and try to figure out who will be top cat.

If you do see real fights (not swats --- swats are okay) in which they are rolling on the floor, screaming, and fur is flying, I would let them continue to learn about each other as they are now. If real fights begin, I think you will need to separate them and start over using the introduction method found here.

This helped, thx!