Daishain’s 5e D&D RPG Main Thread - Page 838 The Sage says...
It looks like there are signs of recent passage through both of the smaller doors.
The big double doors are another story, it is obvious they didn't pass that way, but that is likely not by the cultists' choice. Whatever has caused the doors to bow out warped the hinges. It appears possible to open the door anyways, but it will not at all be an easy affair. Poljen, Velon, and Taz at their best couldn't manage it alone.
Zarra still does not receive a response, but nothing happens if she passes through anyways. She does not receive the warning in the hall with the statues however.
Out of Character: Seath, Lawrance has the historian feat, which among other things lets him add +3 to a roll if he passes a DC 15 history check.
Also, guys, I've updated the map spreadsheet to show your progress. The link is still in my SRD page. The section in green represents the ruined copper doors.