My recently turned 16 y/o daughter is pregnant. Advise?

This is a long story. I am 37 y/o father of 3 girls at 8, 12 and 16 y/o. My ex-wife moved to Maine I think and left the kids with me. I hasn't been easy but I have managed with the over the top help of my fiance, who has a 15 y/o daughter of her own (her father passed a couple years ago). So I try to help as much as I can to be a father figure without stepping on any toes. It is always a very delicate situation in my home. This should go without saying but, I have not brought up many other things like cramped quarters, budget and often thinly stretched patience or lack of hours in a day. Did I mention the cramped quarters? Now, onto my point or need for advise if you will. I had started to have the safe sex talk with my daughter about a year back when she was new to being 15 year old. More recently, as in 3 months back, she turned 16 and I gloated as I started teaching her to drive on her brand new restricted permit, I glowed as a father as I started to take her around and fill out job applications for her 1st job. I must admit I wanted to get her a job primarily to curve her interests away from "the wrong" group of friends and her awful boyfriend whom is currently 15 and on probation after his juvenile detention stint with court required "membership" at Southwest Florida Addiction Services (SWFAS) for alcohol problems. Don't get me started on his failed excuse of a family, mom/aunt with addition problems and another 3 y/o child that she can't care for, his nonexistent father and so on, you see where I am coming from and I am sure you know what type of behavior you get from a boy like this. Late phone calls, being at my home when I get home from work and again so on and so forth. My method of getting her away from this was starting to work as she had been broken up from him for weeks from what I heard. Daughters don't feed to much info to dads. So I felt lucky to have 'heard' that news. I digress. My ex-wife used to live near here, before leaving the girls with me and bolting a couple months back. She also used to have weekend custody as she could not handle any more responsibility. Then all stopped.... I'm not told, however yet again i 'hear' my 16 y/o daughter is pregnant by none other than... you guessed it. I have been unable to hide how adamantly opposed to her having a baby. This also was working in my favor until "supermom" shows up. Now my daughter wants to have the baby, is angry at me for not showing "support" and wants to go live with her mom's mom (grandma) who has supposedly offered to take care of everything. Her mom is not staying here and will be going back up north but somehow has become the supportive one. None of the above have bothered to call me and discuss anything even after numerous attempts on my behalf to contact them. This is going to be a bad situation for all involved including the newborn but, especially my daughter, my other children, my fiance and her daughter. I'm thinking the best option is to let her live with grandma while I turn into a 'visiting' father which I have never seen myself as. Wondering how that will work out on my responsibilities as i have to consider releasing all control of this. Things like cell phone use I pay for but can no longer Monitor use of, her curfew, well being, the health insurance I will be receiving $1000 detectable bills for, etc. right down to things like breaking the law with damages I have to pay for or live with because she is a minor. I feel like I am holding onto a string of hope when i think adoption. The law protects my 1/6 y/o's pregnancy and I have no say what so ever. I know her better than anyone and I know she's not ready for this. We are not ready for this. I still have kids of my own to raise. I don't know what to do. Please don't leave any advise if you are a 15-19 pregnant girl/new mom, trust me you don't understand. If i wanted your advise i would ask my daughter who would/has told me "be supportive" and "happy for me" in a text. If i have a caller name, like Sleepless in Seattle mine would be F**ked in Florida. Any help?