That's typical for Amazon, Google, etc. You don't have to pass all of them, just get enough of them (especially the more senior ones, although you might not be able to tell who that is) to like you.
Having the interviews in Seattle isn't really that strange. If the Vancouver office is new or small, there simply won't be enough qualified, experienced interviewers there to interview you.
Also, since you believe your verbal communication skills are lacking, you should work on improving them.