Did your vet vaccinate them for FIV too? That can also cause a false positive on the test. If they haven't been vaccinated for FIV you probably want to go ahead & get it done now that you know they're negative. Hooray!
I'm so happy for you! Hopefully Snow White will retest negative too.
as i was reading the thread, i was getting nervous my self, i am so happy for you and them, this is such good news i think i will call it a night and go to bed, i like ending my day on a good note and this one is the best