Too much help - my kitchen
If it's not your kitchen, you really can't tell them to leave it alone.  My approach is to save the "serious" cooking for when I am alone, or in my own home cooking for my family.  When I am with extended family, or at a friends house, I try to think of cooking as more of a social activity.  Give people easy jobs.  This politely clarifies roles and ensures anyone who wants to be involved can be.  For the smoking, maybe a small sign: "Please ask me why you should not open the smoker."