It seems that while most parents may sort of realize their children are out of control, they simply do not want to admit it. It SEEMS as if it is a problem with pride or fear.... 
 
My brother's daughter is an absolute brat! She never had a set bedtime...and kept the whole house up for hour upon hour... She screams and yells and then sneaks.... 
 
But then, when I look at the entire house, I see that she is merely a symptom. Their whole house is disrespectful...loud...and out of control! Nothing is sacred! 
 
I am no expert, but I honestly feel that if children are not shown and taught respect, then they will show none! If they learn to respect others, then they learn to respect themselves. And how do we teach them respect? By example...and by being PARENTS....in other words, showing them where the line is and not letting them cross it! If we say something, we had better mean it...even with punishment....that is showing respect! We need to show manners and to teach them. We need to respect others and to teach our children to do the same. 
 
Take a lesson from the military...and tell your sister to do the same....everytime those twins act up....have them do pushups...have them do a chore.... And no second chances! Put them to work...no matter how young they are! They will learn. 
 
Believe it or not...this is something people use in training aggressive dogs as well! If you teach a dog a trick, everytime they show aggression, you make them do that trick. It teaches that dog who is the master and they eventually back down. Now, why I am not saying that children are like dogs...there is wisdom in that technique! Children who own and run a household need to be reminded who the parents are.... 
 
THAT is respect!