two people have told me that they believe the sibling rule still only applies to Bucks Children, and that we would then be considered lower down the admissions table.
Maybe the two people who told you that should actually read the Admissions Policy? It is crystal clear that siblings take priority over catchment. (Not to mention the fact that it would be illegal under the Greenwich Judgement 1989 to give priority to Bucks children solely on the grounds that they live within BCC's administrative boundaries.)
Where eligible applications for admission exceed the number of places available at the main point of admission, the following criteria will be applied in the order set out below to decide which student to admit:
1. Looked after girls and previously looked after girls1.
2. Students who qualify for Free School Meals2.
3. For the main point of admission, siblings3 of girls in Years 7 to 12 at Aylesbury High School who are on the roll and will be on the roll of the applicable school at the time of the proposed admission.
4. For the main point of admission, siblings of boys at Aylesbury Grammar School who are on the roll and will be on the roll of the applicable school at the time of the proposed admission.
5. Girls living in the catchment area of the school.
6. Once the above rules have been applied, and if there were to be a tie within any of the above rules, then any further places will be offered in distance order,
As an aside, on the Admissions page for AHS there is some extremely helpful information about where current pupils of the school live, how many girls might come from state and independent schools, transport to Aylesbury, etc. Well worth a look, and well done to the school for providing such details http://www.ahsonline.co.uk/Admissions