The body doesn't matter in Trench, it's the soul that does, so if Sansa was projecting herself into the seal, she wouldn't see/experiencing anything new.

Ravens would know the same information about zealots that a human could gain from just talking to the zealots or people who were around the last time the zealots showed up. They wouldn't be able to find out/know anything more about the wasps than is already presented.

Yes, they can have more than one person!