Hey! So your internal mark should come from internal assessments in EX2, as it would for any other course (EX2 students, feel free to correct me). Your external mark (again, correct me plz) comes entirely from the external marking of your major work.
That internal and external mark is used, moderated and scaled exactly as they would be for any other course. This guide has the details
Yep, that's correct Jamon.
Whilst it might seem unfair, especially as schools can have weird processes, English Extension 2 is just as much about the journey as it is the destination. However, if there are serious aberrations (e.g. you come 2nd internally and get 45 externally, and the person who came 1st got 25 externally), corrections can/will be made.
The only thing of note with English Extension 2 is that scaling is done solely against the 2 Unit Adv. paper, as opposed to other subjects which are done against all other subjects (that must be a really, really big set of simultaneous equations).