Is there a way to see all completed quests or a way to check off quests that have been done?  Im a bit of a completionist and since I am at the point where the main story is done, all marriages are done and every possible pregnancy has taken I wanted to make sure I didnt miss anything.  

In the quest log, you can switch left/right to toggle between active, finished and failed quests.

The quest list in the wiki can be sorted by alphabet or by their quest ID number in the system, in which I think the quest log also sorts them: https://renryuu.miraheze.org/wiki/Quests