I am trying to understand how will I be able to disable \"pull requests\" in github.
Question 1: We are trying to use the rebase workflow and that means using pull requ
You can't setup branch permissions with Github. However, if you're the only one with push permissions, you don't have to forbid the creation of pull requests: you could just rebase and push them manually.
A tool which my fit your needs is Gerrit. It's an open source software which act like a kind of wrapper around Git. It's mostly a code review software. But it will also allow you to define permissions per branches.
However, a difference with Github, is that you'll likely have to host it yourself.