Hi, sorry to hear about your families illness. I am a nurse, now working L&D but used to work peds. On average incubation is 14days, however, it can be anywhere from 9-21days. It is passed through direct contact with the blisters or through repiratory droplets like a cold. Have any of your kids had the vaccine, that often prevents the virus, but on the rare occasion someone still gets it it lessens the illness. Some people just have an immunity to the virus too. How old are you kids and who does not have it yet? That can play a factor as well. It is possible that the one without has an immunity and will not get it, will develop it in the next week from the initial exposure, or did not get a significant enough exposure and may get it from this new case which would be 9-21days from now. You are no longer contagious once all leisions are crusted over. The problem is that from the 1st day you break out you develope new spots for the first few days so this can lengthen the time. Are you flying or driving? Airlines will not let you on if your child has visible leisions and if the are still visible but all crusted they may require a medical note stating the child is no longer contagious. You should be in the clear except the third child. Feel free to PM me if you have other questions. I really would be interested in how old the last child is and also if they ever get it. Good luck.