Thank you for your replies. Yes, I did indeed get a new litter and keeping them separate all the time now, as I was feeding them together after the op. thinking they can associate the good feeling of food with being together, but was not working well for Zahira as she was gulping up all the food and then throwing up immediately.

Nina (the mother) is a feral cat, a lady got her in her house so she can give birth to her babies. She never got very used to us either, as she gets spooked very easily. One moment she is letting you stroke her on the next stroke she runs away as if you're beating her up. I never encountered a cat so afraid and unstable as her. If the door bell rings, she will pee straight away on the floor. Zahira though is the Mojito cat of the house, she chills with everyone and comes to Nina's rescue all the time when she gets spooked. If she is sleeping on the bed and I stop by to stroke her or just talk to her and she's on guard, Zahira hurries by, starts to groom her and calms her so that even I can stroke her then. Zahira is Nina's chill pill. Now things have changed drastically, they seem to compete on who takes our attention, who ownes the bed and sleeps with us. Nina seems to be competing for everything with Zahira and not letting her close to calm her, she is a loose cannon at the moment. Zahira is so stressed she is now grooming my hands every evening and morning as if I was Nina, until it burns.

Hope this is a transition though as it is so stressful for all of us.