I am sorry for your dilemma. I would keep these cats strictly isolated. I would repeat the FeLV snap test and perform a FeLV IFA in 2 months. If either one remains/is positive then your kitten could still expose your other cat. 25% of these cats convert to negative on both tests (safe), 25% become positive on both tests (typically soccumb to the virus and more common in kittens), and 50% remain discordant (where the results of the 2 tests are different and the patient may never become ill). Unfortunately, these discordant cats are still potentially contagious. Good luck.
Christine Simon D.V.M.