Sorry to hear about your kittens. Yes cats can return a positive Feline parvovirus (FPV) result whilst not showing any obvious symptoms. Your kitten might survive if he/she is treated early enough, has a strong constitution and does not have any other health problems. Whilst FPV is a killer, vet-science has made good progress in being able to successfully treat FPV if treatment commences early. The virus is progressive so the earlier you seek treatment the better. Your other kitten who is not expected to live might very well have a weaker constitution than the other one. FPV is also sometimes called Feline Infectious Enteritis (FIE) and Feline Panleucopenia. It is highly contagious and the virus can live in the environment for up to a year. Catteries sometimes use a Parvocide to disinfect if stray cats wander close by. Ultimately the best solution is to buy a vaccinated kitten, continue with the 3 monthly vaccination regime for the first year and ensure the cat is re vaccinated annually. Some countries require cats sold in Catteries, Animal Rescue places and Pet Shops to be vaccinated against FPV prior to sale, other countries sadly, do not have this law in place. I hope your cat recovers.