Drinking while babysitting

So my sister and brother in law were out of town for the weekend for a friends wedding and I was in charge of watching their 3 kids (6, 3, and 2) I took the 6 year old to her soccer game, took them all home for lunch, took them to the Apple orchard (then a second one an hour away because the first one was closed) took them home for dinner, Gave them a bath, read a book, said prayers, and then put them to bed

Sounds like a perfect day except my twin sister came over during dinner

The problem is that my sister has a really bad problem with day drinking and smoking (probably some other drugs too that she won’t admit) that being said, my sister and brother in law don’t trust her to watch the kids unless it’s only for 1-3 hours.. and even then not so much and just use her when they absolutely have to because she will call them and freak out over the most littlest things like one of them will sneeze once and she will swear they are all sick and that the thermometer is wrong and they need to go to the hospital STAT

So anyway... she came over around dinner time because she’s broke because she spends all her money on weed and started eating the dinner I made for the kids.. it wasn’t that big of a deal because I made plenty but still it’s the fact that she came over just for that not even the kids

Then she opens up the fridge and sees beer and other drinks and wants to grab one and I told her no because if she was going to be around the kids with me then she’s not aloud to drink and she told me that my sister and brother in law told her when she babysits to feel free and have some beer and what not which I know for a 10000% fact that is not true because my brother in law told me that if he ever finds out she does stuff under the influence of any kind while with his kids then that will be the end of it... well she told me she does drink while she watches them and is acting like it’s the most normal thing on the planet

The problem is that my sister and brother in law are coming home today and are probably going to be hung over because it was their best friend’s wedding that they have been waiting for to happen for 10 years and I hope to god they partied hard because those two deserve to enjoy their night.... I just feel like when they get home I need to tell them about my twin but Idk if that’s the best idea while they’re probably going to be feeling miserable

I just don’t know what to do.. should I just stay out of it??

Oh I forgot to mention.. after I gave the 3 and 2 year old a bath I was drying them off and getting them dressed and she ended up bathing the 6 year old but the 6 year old has extremely long hair so it needs to soak in conditioner for a few min before you rinse it and she didn’t put any in at all and on top of that she has tubes in her ears and she’s supposed to wear these wax things in her ears to block water from getting in during baths and showers and she told her she needed them but my twin told her that she’d be fine and that she didn’t want to go down stairs to get them... then while I was brushing her hair I found out about all of this and she told me her ears hurt 🤦‍♀️🤬