My specific situation is my 12 year old will ignore my 11 year old completely as if she doesn't exist. It's very rude and it gets my younger one very frustrated and angry. So she has resorted to sitting there and demanding her older brother answer her, getting angrier and angrier until it becomes physical. I've tried intervening, I've basically made it a rule that if he's being rude then she needs to walk away and forget about it...not be so persistent and demand he acknowledge her. And for my son, I've told him he will have consequences to ignoring his sister. I think it's his weird way of having power over her, and I really don't like it. Besides this issue, lately they just do not get along when their whole lives they been like best friends and have done everything together. They do have different personalities, and my daughter can be very stubborn and bossy while my son can be passive aggressive and hand out the rudest looks. I'm so tired of the disrespect between them. They like to blame everything on each other and the whole household feels miserable because they can't seem to be nice to each other anymore.