MystyDreamer,
I have to agree, you definately have a ligitmate reason to be concerned. I too think that your children probobaly know more than you think they do. At their ages, I would think that it would be possible to discuss your concerns that their father has made some bad decisions (all adults do) and that drinking too much is one of them. Give them your friends number so if they should feel threatned or that the situation is out of control they could call and get her to remove them from the situation.
I have talked with my oldest (soon to be 12 year old) about the dangers of drinking including other adults caring for him. He recognizes when someone has had too much to drink and would call another adult or me.
Hope I haven't overstepped my bounds, but I only am saying how I see it. YOU know your children and YOU know what is best for them.
Constant