It depends on that school's population and, to some degree, your ethnicity. The schools have to comply with federally mandated desegregation guidelines, which limit the number of black students at any school. So if you are black and want to go to a school that already has the maximum number of black students, then you are out of luck. There are few exceptions. If you are white and apply to that same school, then chances are good that you'll get in.
Siblings get no special treatment.
The district may cancel permits upon the request of the school for which a SAP has been obtained. The school can present a request for cancellation on the basis of the student's academic standing, discipline or attendance record. You can appeal to the SAP Appeals Committee, but its decision is final. You must abide by those admission procedures. You can select a school with a particular curriculum or environment.