I chose to side with the vampires but for some reason after I do Touching the Sky, this quest never triggers. So now I can't finish the DLC, I tried using the console to fix it but nothing happened, I reloaded a very very old save and the quest still didn't trigger. Is there any way to fix this? I've searched everywhere and found nothing. I also use mods but I'm not certain if that could be causing these problems or not.

Just putting it out there if you haven't used these ones (and not sure if it's going to work):

setstage DLC1VQ07 200

or

setstage DLC1VQ08 10

So I went ahead and tried out the commands, it doesn't reallly get you there just by console command itself. What most likely happened was the game missed a journal entry and got bugged. So if you can provide how old your save game is you can run through the commands manual until you reach the point where she gives you the final quest. Though it's reported on UESP that the quest is bugged.

nope did that, and it didn't work. They say this bug happens because of leaving serana behind or telling her to wait or something. I've had her as a follower for a very long time, I don't know if that caused it but I suspect it did. Regardless, is there anything that can be done at all? Can I snoop around some files and enable the quest that way, without having to do it in game? A save editor or something, perhaps?

Wasn't expecting a fast response but I'll just copy and paste this down:

So I went ahead and tried out the commands, it doesn't reallly get you there just by console command itself. What most likely happened was the game missed a journal entry and got bugged. So if you can provide how old your save game is you can run through the commands manual until you reach the point where she gives you the final quest. Though it's reported on UESP that the quest is bugged.

Basically you going to have to input console command manual but if you want you can probably enable the quest through the construction set like placing an objective and if activated it'll activate the quest. Though I don't know much about the new one. So just to add in that if you you use console commmand to activate the quest without going through the proper commands it locks up the quest.