Montana,
Here is a link to "Workplace Smoking Rules in Montana"
http://www.hrtools.com/pops/P98_05_5200_MT.asp You may want to also contact your local chamber of commerce, town hall, or health dept for clarification if needed.
People get by doing this largely because they go unchecked. If you are bothered by the smoke (and in my opinion - who wouldn't be?), you should first consider having a respectful conversation with your boss about the issue. That being said, since this is your family, you may want to weigh the emotional cost of raising the issue with what you are likely to gain. What would you do if the behavior doesn't change upon your request or if you pursued the legal route to resolve the issue? Is seeking employment elsewhere an option for you? (I am not advocating that you cave in on the issue - just pointing out some factors worth considering).
That's all - I thought I'd add my two cents since my area of expertise is in Human Resources Management in addition to career coaching..I hope this information serves you well.
Karen