New cat in the house

Yep,My little sister brought home a cat.It's a pretty brownish persian cat with a short tail.Not surewhat is it's gender under those thick fur of it.My mom deccided to called it KoKo or Cocoa becauseof it's brown fur.The other cats somehow hated KoKo.My home already got three cats and they didn't give the persian a friendly welcome wagon.Instead,they hissed and scowl at it.Sometimes,they even try to chase KoKo out of the house by making up it climb out of the window.At times,they will get into a noisy catfight.Trust me,catfights are very nasty and a screeching cat is quite frightening.Whenever the cats fight,we have to quickly stop them from fighting before one of them get seriously injured.As a result,Koko is separated from our other cats for the time being until they learn to co-exist with each other peacefully.