I think it highly likely your kids know. I would talk with then about it, tell them you love their father but he has an alcohol problem, he's not a bad person but he needs help.
The behavior of getting drunk in the garage-I don't think your kids could not have noticed this.
bizarre coincidence? all siblings marrying alcoholics, that doesn't sound bizarre or a coincidence to me.
I think you it wise for you to seek professional help. and Good job and Best wishes on the divorce-thats never any easy decision but taking care of you is most important and your son and daughter will eventually thank you for this. You must lead by example because you are a loving mom.