have I made a mistake with adding a new kitten to our household of 2 cats

[mousemole]

We have 2 gorgeous female russian blues who are 7. They are sisters and get on pretty well. To cut a long story short we now have a new female kitten (8 weeks). This is her 9th day in the house and so far it doesn't seem to be going very well. The other 2 hiss at the kitten and run off - almost seeming afraid of the mad ball of black fluff. Have I made a terrible mistake ? I had hoped they would get on - especially as the kitten is female. Will the other 2 accept her or should I accept this has gone very wrong and find a new home for the kitten ?

I had a 5 year old male (neutered) cat when I got a female kitten and he was the same as you describe, hissing and pinning her to the floor and biting her. It's all about pecking order, he was making sure that she knew he was boss. I kept them separate unless they were supervised for about 9 months (until the kitten had grown a bit as he is huge and she was tiny so I was scared he would really hurt her) and they were fine from then on. 3 years down the line they cuddle in bed together and play chase. They do still play fight from time to time but no-one gets hurt.
I've had other cats who have reacted badly to newcomers but they always end up accepting them eventually even if they never become 'best friends'

They will eventuallysort it out - your kitten is a good age to allow this, it takes a few weeks.

Thanks for that...gives me hope !

My cats are 7 years and 11 months - it took about 2 weeks before the older one would stay in the room with the kitten, another couple of weeks before she wouldn't just randomly hiss at the kitten because she suddenly noticed she was there and a couple of months of her very actively tolerating the kitten, she was almost sighing and rolling her eyes, lol.

The kitten adores the older cat, has done from very early on, runs up to het all chirrupy and rubs against her if she hasn't seen her in the last twenty minutes, follows her round tryiing to play with her and see what it is she's doing. The cat accepts this as her rightful adoration and worship, lol, occasionally deigns to play with the kitten and tells her off when she's irritating.

They don't cuddle up together to sleep or anything, but there's no stress from the older cat about the kitten being here now and they definitely work as a team when it comes to hassling for food and chasing other cats out of the garden.

But it took much longer for the cat to accept the incomer than I thought it would

Can I slightly hijack this thread and ask if anyone has introduced a puppy to a household with cats? I agree that the cats eventually will settle down and accept/tolerate another cat (we have done this several times and it has always worked out) but would it be more of a problem with a different species?