I'm at the part in the main quest where I need to talk to both Ulfric and Tulius about a peace council. I've talked to Ulfric and he agreed to come to the council but when I talk to Tulius, the only thing he wants to talk about is taking the oath for joining the Legion since I foolishly started the "Joining the Legion" quest.

I can't talk to Ulfric about joining the Stormcloaks because he just keeps talking about the peace council and I've tried attacking Tulius but that didn't work either. Is it possible to fail out of a quest? Or am I stuck with joining the Legion?

http://www.uesp.net/wiki/Skyrim:Season_Unending

This answers my question in what way?

edit: nvm i see it, i'll see if it works

edit 2: nvm this doesn't help me at all

So you don't want to join the Imperials? Is that what I'm getting? If that's it then you're ok. I believe after you join the Imperials and take the oath, that you can go right over to Ulfric and join the Stormcloaks instead. Go ahead and take the oath so that you can procede. If for some reason Ulfric isn't letting you join, then go back to the Imperials so that you can start the Jagged Crown quest. And instead of giving the Imperials the crown, you can instead hand it over to the Stormcloaks and join them instead.

I hope this answers your concerns but I wasn't entirely sure on your problem.