Visiting Family Dilemma

My baby girl is 10 days old and my grandparents have just made the drive from Georgia to Indiana to meet her. The issue is they are at my parents place where my sister and her two kids live. Two kids who are sick... she says they have "a bit of a cough and are fine after medicine" and already showed up at my place unannounced yesterday with said sick children. I'm incredibly uncomfortable with the idea of exposing my newborn even further to whatever the kids have. What should I do? What would you do?