I'm with Silly Imp. Pets feel your stress etc so if you are upset/stressed about the new kitten, the felines will be too. I just let the cats sort it out and after several kitten introductions over the years, no problems to report. Then again, mine were always allowed outside too..might be worse for indoor felines.
Monkey has been with us for two weeks. Flash still hisses and spits if he comes too close to her but he's been pouncing at Miss Kitty and she seems to be hating him less. Or maybe she's just tired of hissing. Today he went too far though and she did tell him off and he scurried away. Flash may never accept him..she's a bit psychotic. Miss Kitty has been through this more and seems to be adjusting better. And Monkey? He could care less...its just more mischief to get into!! ;oD Good luck.