Suggest Medication For Persistent Cough Caused Due To Dust

I am the mother of two grown sons who both are do it yourself kind of guys. My youngest almost 50 tiled the kitchen floor, and hallway. He has had a cough for quite some time, and has seen dr's. I did not think this was related until today when I talked with my eldest who seems to have the same cough. They both wore a mask while tilling
, but there is dust all over the place, and they are living in it.