I have a lot of experience with FeLV+ cats. If you separate them from the mother, they'll stay negative. If they are negative on the ELISA they will be negative on the other test. The best results may be obtained at 3 months of age. Good luck! I had a litter of positive kittens. In spite of constant exposure to one another, one of the kittens threw off the virus and tested negative. This is really rare.