get you'r mother or sister and teach your kids a lesson and you say if you guys don't stop it i will separate you too and never see each other again

Talk to the school councelor and ask for their advice and if you have insurance (and the insurance covers it) take them to see a psychologist.  

Spanking isn't going to help at this point (they are just too old) so there's no use in that, sounds like they don't respect you and see you as someone below them.  One thing I always make clear to my children is that I am NOT their equal so don't even try to treat me like one, I'm also not their friend I am their mother and they will treat me with respect.  I also never take their side if they've gotten in trouble at school, there is no excuse for back talk to any adult.  My 10 yr old recently back talked to a teacher at school (which is out of character for him), I made him write a apology letter to the teacher as well as apologize to her face.  I started making my children write apology letters to people they've wronged a few years ago.  My 9 yr old has Asperger's and hates writing them so much that he changed his behaviour and learned to control himself a little better, since he does have Asperger's he does have his "off" days but that is to be expected.

In their apology letters I make them say what it is they did wrong and then say that they are sorry for their misbehaviour and a different way they could have dealt with the situation and a promise to try and use the new method, or try to have more self control.

But seriously seek out counseling, they are the professionals and have a lot of resources that will help as long as you are committed to changing their behaviours.

Hi, to my mind you are very highly sensitive with you children behavior, first you try to little bit satisfy their ego, coz children are very possessive to their belongings, first you apply with younger son because he has little higher bonding with you,make him understand that the elder is good one he will help you in your activities and you have to obey his guidance, in this way elder child feel that I am a good one and younger will feel that mom is with me, so there will not be any big differences in their day to day work, and may get attached to each other, make their hobbies relevant to each other in this way they will learn to work together and  peace prevails... all the best....

Hi, to my mind you are very highly sensitive with you children behavior, first you try to little bit satisfy their ego, coz children are very possessive to their belongings, first you apply with younger son because he has little higher bonding with you,make him understand that the elder is good one he will help you in your activities and you have to obey his guidance, in this way elder child feel that I am a good one and younger will feel that mom is with me, so there will not be any big differences in their day to day work, and may get attached to each other, make their hobbies relevant to each other in this way they will learn to work together and  peace prevails... all the best....