Help me with my cat?

My 11 month old female cat is hissing, growling & attacking my 3 young female cats... I have 8 cats all together... but my female cat bella if fine with the older cats - She just attacks her sister and the 2 younger cats... the 2 younger cats are also female the 1 is about 8 monthes and the other 1 is 8 weeks. Apart from the 8 week old cat have been spayed so thats not it... Up untill about a month ago bella and her sister and the other cats used to cuddle up together eat from the same bowls and licked eachother.. but all of a sudden bella has been hissing at them and recently hissing at me.. but when shes in a room on her own and i go in there shes fine with me and puurs and licks me.. its just when she sees the other 3.. But i only just had the 8 week old kitten last week and she was like it a few weeks before that so its not the new kitten doing it. So i really dont know why bella is doing it... she goes out alot longer than the other cats?? Maybe thats why???