cats fighting =(

we have a cat about 7 whose been out only cat for about 5 years and a couple of months ago we got a kitten, they didnt get on and my older cat continualy hissed at the kitten. after a while they got used to each other but the kitten still trys to attack the older cat who doesnt want to play and they fight, which is pretty normal. Only today we have got another kitten younger than our other one. we were more worried about what the other cat would think but she just hissed and walked away. Our older kitten however we wernt so worried about, thinking thay would just play like any kittens would but we were wrong. The older kitten wont leave it alone she is constantly attacking it hissing and being extremely violent, she growls, hits, hisses and bites but not playfully. we try and seperate the two but the older kitten just gets angry and attacks us. she seems to have gotten very very angry and she wont let you touch her. At the moment we have to keep each cat in a seperate room at night and in the day we have to be aware of where they are all the time, the two kittens arnt yet old enough to go outside so we have to watch them all day.

has anyone got any advise on what i should do?

(sorry for the very long thread!)

thanks