by Rubric
The rules give a specific order for starting the showdown (see page 18). The hunting party is formed first, and THEN secrets are revealed.So, yes, the Lair card forces Hanbrook into your party (first), and then he is revealed as evil (second) and joins the villain. You're also correct that Darkest Secret trumps Reluctant.
Regarding the Reaper, I unfortunately don't have it yet. But, your interpretation sounds right to me. It seems pretty straight forward.