Going by their skills, I personally think Reisen would make a better Arbalist, and Youmu a better (Wo)Man At Arms.
Sure, but since Thief/Paladin is the 'starter pack' you get at the beginning of EVERY new game it's kind of fitting. I think I'm right in saying there's even an achievement for getting to the end of the game with both Dismas and Renauld still alive.