Alright so I had a look at your save. The issue isn't actually due to the iberian wedding, it occurs when the Ottoman AI annexes Byzantium which has Athens as a hereditary pronoia.
Note: If you want to continue the save, I have had some success in getting past december with the ottomans annexing them around June next year with no crash, weirdly, so if you are persistent enough you can keep playing.
For the devs: Here's how to reproduce it:
If you go into spectator mode and click onto the Ottomans, you'll see that they are just about to stackwipe the byzantine army which causes them to send the peace-deal in the next month which full annexes them. I was able to reproduce the crash by sending the peace-deal which demands full annexation for Byzantium + Athens.
I tested a few scenarios:
1) I let one day pass so the byzantine army is stackwiped, then I send a peacedeal to byzantium which demands their full annexation + Athens. Result: Game Crash
2) I send a peacedeal to byz demanding their full annexation but don't take athens. Result: Game Crash again
3) I send a peacedeal to byz demanding only Athens. Result: No Crash
I'm guessing the game can't handle removing Athens' diplomatic status as a Pronoia if their overlord doesn't exist anymore... Based on what I gathered from the crash log. I've attached the exception and screencap of the error log when annexing byz.