If someone in the house has the swine flu, is it certain that other members will catch it as well?

No: It would not be surprising since flu is spread by coughing, sneezing, and touching things. It is common for illnesses to go through families and one or two embers not get sick. Good hand washing and a strong immune system can make a big difference. Take elderberry as well as it can boot the immune system and prevent the flu. Having good vitamin d levels also helps boost immunity.