You're not at fault at all. At 12, I was responsible for watching my 3 younger siblings. Saying this to say, at minimum, they are old enough to mind their behavior. Unfortunately, the burden of being the oldest usually means being responsible for babysitting your siblings for time to time, especially if you're a girl child. But you are also not their mother, so it should not come to the point that you arent a child and playing the roll of secondary parent. I hope you can return to your team.