Well since I have exhausted all other resources maybe those with similar experience can help.
I'll stick to facts and keep it brief
My step daughters are going on 13 and 16 in a month and have little if no respect for me and some for their mother. I get tired of hearing "all kids are like that" They wont do anything around the house unless asked and when they do it, usually it is half assed or I had to ask them more than once. The latest is my soon to be 16 year old does not wanna get a summer job, thinks her chores should earn her money and generally is LAZY. Adding her onto the auto insurance will cost us over $700 a year and while I have no legal say if she gets a license I damn well have a say if she goes on our policy.I also at this point don't feel when the time comes I shouldn't have to pay for her college or help with a car as that's what her father is for even though he is a cheap fuck(unless there is a major change in attitude). Their future is set, aside from anything I get from my parents and not having any children of my own, we own 3 homes and 2 small mortgages. They don't appreciate anything. She comes home from school, does what she has to then sits on the couch for "hours" on the computer(what she is doing as I write). I am currently applying for disability due to a failed back surgery and going for another surgery shortly I still do a lot around the house but not what I used to and the 16 yo had the nerve to tell me i need to get off my lazy ass and do something. Believe me when i tell you I am not embellishing when I say i do stuff some cleaning and all repairs and maintenance and remodeled most of the rental house we purchased in January . Speaking to her mom about hours on the computer is a mute point and the last I heard she was failing 1 if not 2 classes. I know what I would do but that's me, there would be limited internet time, limited time with her girlfriend(she is lesbian)until her grades come up but that's me. More recently she has on more than 2 occasions called me an asshole, dick, said fuck you, drunk, lazy, told me to get off my lazy ass, basically anything disrespectful. She is bi-polar but controlled on meds and refuses to see a counselor. Her dad basically will not accept her and he allows his wife to use expressions such as faggie around her. I'm sure it hurts her but I'm sure that's not whats driving her. She did go to live with her father for a little over a year but the grass wasn't greener cause when she came out of the closet he lost it and took her to a hospital.

Her moms biggest fault is not following through, in other words she says one thing then the next day its another. Talk about mixed messages. We constantly fight over this and the younger is already worse than the older one was at the same age, the one that swore she would never be like her sister. She throws tantrums, says OMG(which annoys me0 starts screaming, stomps, throws things, even hit her older sister out of anger. I tried not getting involved and letting them be pigs and heave their mother deal with it when she gets home but that didn't work. I could ask them 100 times to put dirty dishes in the dishwasher but it just doesn't happen, just this morning I asked the youngest why she didn't? she said cause the dishwashers clean!! Really! WTF is what I wanted too scream (that's how tired of this I am) empty the F-ing thing if it's full. I am so frustrated I am at wits end and trust me when I say I haven't even scratched the surface yet. Thankfully I pretty confident they don't do drugs.Any words of encouragement? I do know that my wife and her ex fought a lot and so do we but I always tell her not in front of the kids and one last thing she will always throw me under the bus or undermine me in front of the kids and doesn't stop.