By the time it showed up in the test she'd already been exposed to the others for a couple of years, so the consensus seems to be that they are OK. What they don't tell you about these horrible diseases (apart from many cats having natural immunities to them) is that they can hide from diagnosis until too late to do effective quarantines. We keep the three with FeLV away from the others but we know that it probably doesn't matter, because they were all together for so long before the disease showed up in tthe tests. (After the first tested positive we had them all tested.)
We had most of them innoculated for FeLV but the vets talked us out of it because they are inside-only. I wish we hadn't listened to the vets.
We plan on having them all tested again at some point because it is not uncommon for cats to eventually fight off FeLV and be cured of it, and they're all very healthy except for Jessie, and even she tested negative when the vet ran a suite of tests on her a month or so ago. We were hoping it was thyroid, fearing it was FeLV, not expecting FIP or Coronavirus. (The tests can't really tell one coronavirus from another, all they can tell is that thecat has been exposed to "a" coronoavirus at some point, which may or may not have been FIP.)