OK this is abit hard to explain, but

Well my cat has just had 4 kittens and we also have 2 other female cats in the household and one of those females are the mother of the cat who has just had kittens, well the kittens are about 4 weeks old. But every time the kittens get near there nan as you could call her, she hisses and becomes very nasty, she dosn't hurt them but just hisses and spits at them, why dose she do this?

The other 2 females are fixed and vaccinated the other female cat has no problem with the kittens so why dose the other female, the kittens nan, do this?

And also the mother of the kittens has no problem with her mum, her mother is the only one with this behaviour why is she acting like this?

From what I gathered, the Grandma cat is hissing at her daughter's kittens. If this is the case, then the grandma is threatened by the new litter. She is obviously the dominent cat in the house. Any one of the new kittens can threaten her position within the heirarchy. I don't know if you've seen "Meerkat Manor" on Animal Planet, but the mother meerkat has dominance over which one of her children can have children and will kill any or all of the pups she doesn't want. Right now because of these new kittens, the grandma is probably showing her displeasure with them "existing" if you will. You may want to keep her separated from these kittens, as if you were introducing them for the first time. Keep grandma and the kittens in two rooms seperated by one door. Feed the grandma near one side of the door and her daughter and her kittens on the other side. This way she'll get used to the smell of them and hopefully they'll get used to her as well. As long as she is just hissing and spitting at them it should be ok. If it starts getting worse, you need to contact your vet (which you should do anyway) and find out what they have to say.