Is there goal line technology in FIFA 15 (PC)

That quest is very bugged, yes. Try using http://www.uesp.net/wiki/Skyrim:Console#resetquest to reset the quest completely. Then when you go do it keep the following in mind

1. Go right to the wedding area as soon as you start the quest without faffing about
2. Kill her by dropping the statue on her, everything else is really bugged.
3. You ABSOLUTELY MUST go by (while visible and not sneaking) the entrance to the courtyard (near the door that leads to the balcony) to cause everyone to become hostile to you and that argonian assassin to spawn there and tell you that he will "hold them off" and only then should you run out of the city. If you actually escape unseen the city will become broken.
4. After finishing this quest, don't start the next one until you finish the thieves guild. Because the dark brotherhood is going to put an unavoidable 1500g bounty on you in solitude later on and you could really use that "pay 50% to erase the crime" ability they grant (although if you really wanted to, you could just console away your crime instead... or serve time)

Never add/remove mods from a game in progress. Modding in skyrim is a bit buggy, and removing/adding mods during gameplay fucks up a lot of the scripts that run in the background.

So if you add mod, start over from the beginning. If you remove one, do the same.

Yes, this is very annoying. But sadly that is the only way to keep your games from not being corrupted.

But the important lesson. NEVER add or remove mods to a running game. (as far as I heard it still can crash even with all the additional tools and steps. It is best to not change mods, to keep your save clean).

Call Odahviing to Dragonsreach

First of all, I don't think this is a quest item. I think you mean this as a step in the fallen quest. If this is what you mean.

You could try to use console commands to force the quest to the next step. Look at the quest stages and advance the quest to the last one. You will miss out on some stuff, like the dialogue, and there is a chance that the next quest does not activate properly. But this is what you could try.

Disk space

One possible problem for save corruption is running out of diskspace during playing. Happened to me once. So make sure you have enough space on the disk where the saves get stored. (Default is your 'My games' directory).

Related question

This question has been asked before, see : how-to-fix-corrupted-save-files-in-skyrim

Teleport command

See this question: What is the proper teleport command in Skyrim?