wow! so glad i found this site. obviously i am new here! need to vent a little and am serious need of advice!!

i don't even know where to start....my husband and i have know each other most of our lives. as well as our families. he has 2 daughters (2 different moms) one is almost 18 (lives with us full time mom can't control her mouth, make her go to school) and the other is going on 14. i have a son that just turned 11. we have been together for 6 1/2 years. my 14 y.o. sd is a pretty good kid. she's had it pretty rough-mom has always had a drinking problem and at one point we suspected some drug use, involved sd in all court proceedings(it was sickening what this child was told)-that's another story. after 6 years of court proceedings we were finally granted residential custody. and we have her a majority of the time. this child is not my problem (child). she's helpful, talkative, sweet she has many wonderful qualities. my problem (and everyone in our house) except my husband are having difficulties with the 17yo. she is so unbelievable slick!!! she is just a princess when daddy is around. the minute he leaves a room or the house it is like a completely different person!! she is mean, nasty and disrespectful to me. she is physically abusive to her sister and my son. she has literally pinned the 14 y.o sd to the bathroom floor and left bruises, welts and scratches (my son witnessed this) both of them where threatened if they told she would kill them. it took quite some time before either of them confided this in me. neither of them will stay home alone with her. my son is deathly afraid of her. when anyone mentions something to my husband about it he tends to think my son provoked it or the 14 yo is lying. my son is not an angel but does not deserve the abuse he gets from her.
she is beyond lazy. her room is so far beyond disgusting i think i may have to burn it when she moves out. she creates more and more work for me. leaves dirty dishes, clothes, garbage etc everywhere around the house. she complains to everyone her life is so difficult. (when she turned 16 she was given a car with the request she get a job and pay her gas and part of her insurance. she finally got a job in june but still won't pay part of her insurance. she doesn't like the hours. her mother feels guilty becuz she doesn't spend alot of time with her so she takes her shopping constantly (she will walk in with 6-8 bags of new clothes and trinket crap several times a month)
i have caught her in numerous lies and somehow she always talks her way out of being in trouble. when she does something wrong i think there should be a consequence. my husband is unable to stick to a consequence with her (my son is a different story)her car was taken away for getting a speeding ticket (we knew the officer that gave the ticket)and he was going to let her off becuz he is a friend but she was so snotty and disrespectful to him that in the end she got the ticket(that was on a friday) by monday night she had her car back.

my in laws are quite fed up with her disrespect to them and the antics she pulls. they all bend over backwards for my son and other sd by picking them up if i (or my husband)won't be home so neither is left alone with her. she has physically hurt the nieces and nephews varying in age from 5-17 y.o. no one in the family will allow her to babysit or spend time unsupervised. why is my husband so blind to how she treats people? he is always convinced it is everyone else's kids fault. i am (so is sd and my son) hoping she moves out to her mothers as soon as she graduates.