I just don't get it. . .

This coughy cold thing that we have been having I just don't get it! Here is our calendar of events:

February 4 - 9: Kevin has fever, cough, and stuffiness for first days, the cough and cold linger the rest of the week.
February 12-14: Josh has fever and runny nose. A little cough. His nose continually "drips" for another week or so.
February 14 - 19: Sam has fever, cough, and stuffed nose. Cough lingers still.
February 14-?: Rachel has fever, cough, and stuffed nose first few days. Then loses her voice, and still now has a stuffed nose and lingering cough. Pregnancy makes it harder to get rid of a cold but hoping it is gone by Friday!
February 24 - ?: Josh is coughing again! horrible hacking coughs that he coughs up phlegm, and of course his nose is running again. Is this the same cold? Or is a new one starting??? I JUST DON'T GET IT!