1. FB preference 4 takes 11 years now, so it will take more than 12 years to get GC through your brother.
2. 3. 4. Not much faster if parent now apply GC through your brother and they apply for you after they get GC if you plan to marry in the next 10 years.
6. you need to keep your own status (without their help) for the next 10 years or so, or wait outside of US.