You guys are breaking my heart!! Mine are 18 and 21 now, but boy do I remember the days......... As I said before in other threads, I used a lot of Cesar Milan's dog psychology on my kids.
Firm, tough LOVE - lots and lots of love. But I am the boss, albeit a fair boss.
Our cardinal sin in our house was lying. You could get through the discipline of whatever you did if you owned up to it (IMO the biggest lesson in life). Lying got you into BIG trouble, and they learned that early. I think you're doing a GREAT job trying to be firm and fair. It's not going to feel like you're winning at the time.... only will you truly believe that you were a good mom (who, by the way WILL make mistakes along the way) until they are grown. Up until then, you just have to keep at it and have faith in yourself.
The talking is frustrating... but remember, of all the things you could be dealing with, that's something that you can get through......
Hugs to you to get you through. I'm so impressed!!