Growing Pains

My husband and i married 2 years ago, he came with 2 children. Currant ages: girl 15, boy 13. I came with 3, girl 17, boy 12, girl 10, and one together boy 3. We have been together for 4 years now and what a crazy, wonderful, hurtful, scary, awesome time we have had so far! There is so much to share of our story that i could type for hours so let me give s much info in s little time as possible. In the beginning : became pregnant, moved in together, shortly after baby came my eldest moved in with us also. So we became a blended family of 6 children 2 parents. By year two we started to struggle with my eldest daughter whom presently has chosen to live on the streets due to our different ideas on rules and expectations and issues from the past. About two years in my husbands ex re joined the picture and the hole every other weekend and such began. My husbands youngest boy 13 went to live with his mom the beginning of the school year. A very hard change for my husband a specialty, he has never not had his kids. When him and his ex separated the children went with him he has guardian ship ( full ) still to this day! So now his eldest girl 15 has decided she wants to live with her mom also. The issue stems mostly that in the past years of this teens life her and her mom have had a very strained relationship. Her brother being " the favoured" and the baby. She has much more memory of what happened and understanding of the past. Our parenting styles are polar opposites were we have rules: respect, honesty, do your best at what you do, a do what u must but be prepared to face the consciences attitude! Her mom has more of a do what you will and if you get caught we will talk about it. Not that we dont agree with talking about stuff but there is a time and place for the consciences when just talking becomes redundant! Girl 15 has recently taken that dreaded change that most parents dont want to see, she has gone from being pretty much an A, B student to failing 3 of 4 classes, change of friends, and doing drugs and alcohol. One of the hardest parts is knowing she wants to move to her moms because she will more or less be free do do as she pleases with no consciences! We have tried to talk with her but she is hell bent on moving to the point of what seems to be going out of her way to make our life's a living hell! We are afraid of losing her, we know we will still see her but, the shift in attitude that happened in just one weekend is crazy! We cant imagine what it will be like full time? Also, im feeling like what if we had not married would things be different? Both of my husbands kids have now chosen to move with their mom. The younger of the two was also very hard but for completely diffirent reasons behind moving, he has always been a moms boy and has held out for her, and now getting needs met that otherwise un reachable to the depth he needed. Where as girl 15, has repeatedly stated that she has not wanted to move in with her mom full time due to the lack of parenting and the I'm your friend attitude! I know blended family life is tough but i had no clue it would be this heart wrenching . I have put my hole heart and spirit into this kid for the past 4 years, wile her birth mom couldn't be bothered to even call! This really sucks! Help!!