Damnation feat questions

[Murdock Mudeater]

With Damnation feats, do the effects granted by each "level" stack, or replace each other? Like, with 2 damnation feats, do I gain the benefits from 1 damnation feat and for having 2 damnation feats, or just the current total.

I've read it a few times and I think they stack, but I'm not sure. Can I get this verified?

Source is champions of corruption. I do have a physical copy.

There's only 4 total damnation feats. When looking at them, "soulless gaze" and "Malficium" seem intended to stack, "Mask of Virtue" does not. Unclear with "fiendskin."

[Paulicus]

Seems like they all should stack to me.

[Murdock Mudeater]

If stacking, the one I'm unclear with is fiendskin. Assuming my "patron type" is devil, as I read it, I should end up with Immunity to Fire, Immunity Acid or Cold, and Resist 10 to Acid or Cold (opposite of the one with the immunity). I also change my type to outsider (native).