The first mom was simply a suspicion. Let it go and keep an eye out. She may have been nervous, intimidated, or have some ADHD issues of her own. Find her something to do that fits her.
As for the second...Good for you for speaking up! As a mom of 3 and a former Police Officer, this is what I would do... First priority has to be the kids, our whole purpose. School is a place for children to be safe & see healthy role models, never a place for any amount of alcohol. She plainly admitted to drinking 4 beers before the meeting. Wow! I don't know about you, but for me, 4 and I think I would be almost unconscious! The school couselor is an excellent resource & an absolute must for the children's sake (bet the counselor won't be suprised either.) Next is the Principal, they simply need to know what happens on school grounds. Finally, call the police if she drives too or from the school. Let them decide what to do. They have full discretion to help, assist, or arrest this mother. They may also be aware of her (and her children.) Most of us wouldn't think of driving under any influence of alcohol, yet alone with our children, but know that many do! So, take a deep breath, stand up straight (because you're obviously a wonderful person,) and let those who can help intervene & get this family help. Be a friend if you can, don't let anyone continue to bad talk her (you never know what another is going through), but point this situation in the right direction where a someone who can, can really get involved with the whole family. If no one seems to listen or care, you can call your County's Child Protection Agency to simply voice your concern. They'll listen.
And thanks for caring, you may just change those childrens'life for the better!