Cat Fighting New Cat?

  Hi, we have three indoor cats (female - 19 years old; male - 10 years old; male - 1 yr. Old). We recently adopted a stray female cat (about 1 yr. Old). She is currently an outside cat, although she comes inside for meals. We would like to bring her in permanently, but the 10year old male physically attacks her. She does hiss and growl at the other cats; and they at her ... but the older male is violent. He gets along ok with the other cats and has never fought with any of them. We have had cats (including the inside three) start off not getting along; but never physically harming each other. Any suggestions on getting some peace and acceptance between them all?
First of all, NEVER JUST BRING A NEW ANIMAL IN! Cats, (and dogs), need to meet a new pet in small doses. It's natural for cats to fight if you just bring in a new pet randomly. If you let them meet each other slowly, they'll be 'friends very fast. I hope your cats are neutered/spayed.
Two of my cats are best buds. They romp and play and have a good ole time . Recently one of them was in the hospital for four days. When we brought her home her buddy hissed at her. This went on for about four days until all the strange smells dissipated. There is a product called "Feliway" There is a spray and a plug in. It is somewhat expensive. It is pheromones that calm cats. It works.
Is your 10 year old male neutered? Also, you need to get the stray female to the vet and make sure she's spayed. The 10 year old is probably the Alpha cat and might just be looking out for his "family"
i had a 4 year old (boy) cat and then i got a little kitten (girl) and they were fighting the boy can was an outdoor cat and the girl was an indoor cat and this year he ran away or got stolen: (
http://cats.about.com/cs/catmanagement10 ... Here is a website that might help out a little. I know it can take some time to get them acquainted. Good luck .
let it get used to it