I hear you. I have a step son who is 17 and one that is 14. I am always the one to blame for everything. They do stuff when their dad is not watching and put me in a place I don't feel comfortable. They act sometimes horrible at our house and calling me names that are not nice at all if they don't get their way.
Their mother didn't do much with them for 2 years, now she is losing her house and we are moving into it. I just feel resentment all the time, and it needs to stop.
I do a lot for them boys and I do love them, I just don't love their behavior. I think a lot of it has to do with lack of rules living with her, and we have rules here for my son (who is 15), the same rules should apply to them too!