Re: can someone help me out
Sounds like their big problem is you smoking and not necessarily the location - given that there's another family member staying in the house and smoking cigs. I'd just keep it quiet by doing it outside or elsewhere.
If it's just about the smell of the smoke, introduce them to the smell and explain that it doesn't have the same raunchy smell that lingers in the home.
"The test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function". - F. Scott Fitzgerald