SureAI

After I put in the two passwords, every save file i make after that point is completely unusable; they crash before even loading into the game. Is anyone else experiencing this? Because I've tried to go through the castle 5 times now. And if i die it forces me to load, of course, but every time i have to go farther and farther back in my saves because it ends up refusing to even read before i put in the passwords. The only safe place for me save-wise seems to be just outside of the castle.
Any help is appreciated.

The spell "Mage light" could cause the crash if you used it inside the castle. If that's the case use another savegame before you enter the castle. You could also try to disable autosave in the Enderal Launcher, this might help you too.

Let me take a look at your savegame. Attach a savegame (as 7z, zip, rar):
Savegames can be found here: documents\mygames\skyrim\saves
A savegame consists of two files: one .skse and one .ess (please zip them together)

Thanks.

I did have light on, yes. I will try going through again without it. I will go ahead and upload a save regardless.
Attached is a save from before entering the passwords.

The magelight was 100% the problem. I loaded the save until it didn't crash, opened the console as soon as it loaded into the game, and banished it with console commands and it didn't crash at all after that. Thank you, that was a rather odd fix.

I'm glad that this worked for you. This is a known bug, currently (as far as I know) the trigger is unknown.