@Jen001 I always credited my library job for my (previously) robust immune system. What is the first thing people do when they are sick? Borrow a book and sit on the loo sneezing while they read it. Then return it covered in snot.
Seriously though @Nicole69 it's not the people who you know are sick that are the problem. Many diseases are at their most contagious just before, or at the same time, as the first symptoms appear. Someone who is getting over a cold or flue is less risk to you than someone who has the first signs of the lurgy.
Common sense should prevail though, if one family member has been ill, it's likely another is about to be. Wash your hands and don't let any of them lick your face. Mxx