Hello and welcome to the forum!
First of all - when checking saves, we require both .ess and .skse files, please upload them in a rar/zip archive.
Have you used console commands like the ones you mention before to complete quests? That alone is enough to break quests in unfixable ways.
Do you use mods? If so, try and disable them, or if you don't, try to load a save before you are start the quest and re-do it. (I hope you have a save that goes back that far...)