Huh, I hadn't thought about the five stages of grief, that could be very fitting for this adventure. I also like the idea of going along the emotions as they travel. Mine was based off Plutchik's wheel of emotions and something I read about random emotions early in dreams.
In Pirate Borg only PCs get bonuses to their rolls, so they should have an advantage against doppelgangers. Plus I see the fight against Mourn as a naval combat, so they'd be using their ship's stats. And yeah, either way, there are multiple ways to regain hit points after or during fights.