Why is this happening to my kitten?

Ok so a while ago my cat Skittles had 3 kittens. We gave one kitten a home. But we couldn't find the other two a home so we decided to keep them. So now we have three cats. Just recently we got Skittles spayed and her other older kitten spayed too. We couldn't get the younger kitten spayed (she was the runt) because the vet said she didn't weigh enough. So now I recently got attached to the girl kitten who got spayed. But Skittles and her other kitten started ignoring me and my family. They also turned against the kitten that has gotten attached to me! They hiss at her. They run off from her and try to avoid her but the other kitten doesn't do anything to them. She's nice to them even though they are mean to her. But why are they doing this all of a sudden? Now Skittles and the younger kitten are ignoring me and my family now! They won't go by us or they run off scared. But the kitten I got attached to plays with me and cuddles with me. She's always at my side. But what about the other two cats. They always hiss at my kitten. Why do they do this all of a sudden?