First off the problem is with his kids right? If so, then why are you contemplating leaving? Your DH has to have a talk with his children and let them know that there will be no choosing one over the other, that the choice was made to have you as his DW and they are his children. Your DH should make clear that he will not accept any disrespect toward you and they are to treat you civily.

There is nothing you can really do, the ball is in your husbands court, so to speak. Either he sets things right or there will always be problems. If he can't get the kids to obey then he will have to decide to limit contact with them. Believe me it won't take the kids long to figure out how to act if they want to be with Dad. Kids try to see how far they can push and get away with things so, a litle bit of Dad setting limits is in order.

My advice is for you to stay out of the "choosing" zone and let your DH take the lead on this. Tell him how you feel about him and your relationship. Then tell him how you feel about the kids treating you disrespectful. Do this when the time is right not when the kids are there and he is under pressure.

The love you have for each other should be stronger than ability of the kids to turn you toward leaving each other.