Hi Tina - sorry to hear you are in this situation. I can understand that you are reluctant to lose your studio time and possibly offend.
There is nothing mean about looking out for your health (and that of your friends!). It's obvious that they are NOT aware of "all that has to do with torching" or that they are deliberately choosing to ignore the possible health consequences.
There are a lot of great references out there explaining exactly why good ventilation is so important. Maybe send them a link or two?
http://www.michelsun.com/art-blog/20...tilation-guide
http://www.frantznewsletter.com/2010...t-ventilation/
https://mikeaurelius.wordpress.com/2...-one-overview/