Rise branching scenario

You can't adjust the built-in Menu to only show some lessons but not others. I suggest you turn off the Menu completely. That's done in Theme>Navigation>Type:

• As needed, you could include info in an Intro lesson about the outline of the course.

I'd also suggest turning off the automatic prev-lesson/next-lesson buttons.

• Instead, use button blocks to connect the lessons.

As for completing the course, you could route the quizzes to a final lesson that has a Storyline block with a Complete Course trigger.

• To add Storyline to Rise, you first publish the Storyline file to Review. When you do that, indicate that it should be tracked via the completion trigger.
• Then, when you publish the Rise course, indicate that tracking should be done via that completion trigger in the Storyline block. 

(Personally, that's the kind of course I'd do in Storyline. That would allow you to track completion via whichever quiz the user completed first, which, of course, would be the one in their chosen specialty.)