help... new kitten doesnt like my other cats..

i have two male cats one 7 months one 2 and a half.. they get along perfectly.. they are each others companions and play all day.. recently i just took in a new cat which is actually my 2 and a half month old males sister.. a friend had to get rid of her so we took her in.. but she will not get along with my other two cats.. they walk up and sniff her, my older male even cleans her... but all she does is growl and hiss.. her brother left her alone at first... because all she would do is hiss and growl... but now he has started chasing her and biting her... if she is not going to get along with my cats i'm afraid i'm going to have to get rid of her. what should i do?

thank you

You've got to give it some time. I'd actually be THRILLED if my resident cat was grooming the newcomer. And the chasing and biting is probably just play and "establishing dominance" behaviors.

Exactly how long have you had the new kitty?

They are all fairly young, so chances are they will end up getting along just fine. Of course "just fine" could just mean a uneventful co-existence - she may not be best friends with everyone, now or ever, and that would be just fine. In essence, we have to let our cats decide on dominance issues, and the level of closeness between them.

One very important tip is to never ever yell at or around the cats or punish them for anything when they are together. You want them to always associate each other's presence with positive things. Try to keep calm and relaxed around them and not to stress over their interaction issues (easier said than done, I know, but we have to try!).

You could also try making mutual presence even more fun, but providing special treats when they're together. Make sure you give the treats out liberally and not too close to each other. You want the cats within eye distance, but not too close, so they don't end up fighting over the treats.