It's OK to discipline someone else's kids even though their parents are right there?

I get so anxious when my sister in law pops up with her 5 kids. First of all my house is tiny so adding 6 people in here already makes me anxious. Then her kids start arguing and yelling at each other, hitting each other, throwing my daughters toys everywhere. The older boys and the 6 year old girl will sit on toys meant for a baby.The almost 4 year old twins are left totally unsupervised since their mother sends them to my daughters room where they wreak havoc. Their mother is totally oblivious to all the screaming, running, crying, tantrums, toy throwing, etc. Friday me and my family went to Big Boys with them for her oldest sons birthday. She was totally ignoring their screaming, they kept getting up and walking around, climbing under tables. One of the 4 year olds wandered off and her mom didn't notice right away. My hubby's mom starts screaming at the 6year old and the whole time MY husband is trying to get the kids to stop acting like hooligans and to get his mom to stop screaming, while the kids mother is ignoring everything. We ran I don't know how many people out of the restaurant. I get so anxious and I feel like I've lost all control when she brings them all around. The messed up part is when their mom is not with them they do whatever we tell them to do. What do you do when the person you are with will not discipline their maniacal children especially in a public place? They aren't my kids to be worrying about.