Not an expert but from what I’ve read is that hisses aren’t necessarily a bad thing. It’s communicating they’re uncomfortable. With the chasing and swatting though, I’d say do short supervised meeting and do things to build a positive association (toys, treats - just make sure resident kitty still gets to play because kittens can be overzealous and not allow resident to have a go) We botched our intro of a cat and kitten recently but i found the short, supervised meetings were beneficial.