Need help with filtering data

created this app to use with my schools. The idea is to have someone go into a classroom and provide feedback while in the classroom. So, here is how the app works:

starts with picking the school, then grade level, then subject. However, when choosing subject all the teacher that teach that subject appear in the list. I want it to only show those teachers that are on that campus that teach that grade level and subject.

for example:
school - western hills
grade level - 3rd grade
subject - science
should only show Christian baxter (currently, it shows all teacher that teach science)

How do it get it to show only the teacher at that campus, in that grade level, in that subject? Please help.

I have replied with a bunch of questions in the other duplicate topic on this subject.