Full time mother/step mother to 5, not coping

Hello to everyone! I don't know how to start this! So much I want/need to say, yet I don't know how to put it into words!
My partner and I have been together 5years, married 1, I had a boy 4 and girl 3, he had a boy 4 and girl 3 when we met, since the start it's been stress after stress around the children and his ex, either our kids clashing, his ex withholding his children and my partner suffering bad depression due to that, going to court and spending money we didn't have (we were living with my parents) we lost in court and his ex moved hrs away, my partner then started working FIFO (2011) we had a baby together 2012 and his ex moved back to town now with a baby as well as my partners 2 children after that relationship ended. She began drinking heavily and we even at a few points took the baby when we had hubby's 2 children just to make sure he wasn't left with her whilst she was intoxicated, she has suffered a bad childhood but was continuing the cycle of abuse, we didn't know how bad it was until she moved away again (2013) and when that relationship broke down was picked up by police with her then 2yr old half naked in the cold walking around extremely intoxicated. She was warned at court. Child protection was involved but because My husband was out of the country due to work we were not even notified. Back and forth a few months all 3 children are eventually removed from her care and we get a call at 8pm from her local police station because they had the three kids, I sent Hubby up to get them while I stayed with my 3 and told him don't leave the little fella on his own bring him here (his dad wouldn't take him and had no family that would)
So we go from 3 children to 6 children full time. 3 sets of twins you might as well say. My partner works a month out of the country at a time when all this starts happening. Eventually through court etc it's decided the youngest will live with his Aunty. I feel guilt of not being able to have all 6 myself.
My partners children have been exposed to so much, sex, intoxication, emotional abuse, even physical abuse a couple of times (hit with a broom) logically I understand why they are the way they are. Emotionally I don't deal with the stress. My step son (9) has sexually interfered with my daughter (7) more than once (found out much later, this has happened when he was 7 and again when he was 8 ) I feel like I don't have the "right" to kick up a stink about it because it had happened so "long" before we found out. I have finally got him seeing a child psychologist and he has been diagnosed with sever hyperactivity to the point of medication being recommended, he always talks, doesn't sit still, doesn't let you finish talking, never slows down enough to do anything properly and often wrecks things/breaks things because of this. He was chewing on my kitchen chairs and putting holes in walls at 8yrs old, he will physically attack both my older son (9) and my daughter (7) he was choking her just the other week!
My step daughter is a very soft spoken child who had delays with speech, concerns with her learning that were never followed up about, and has fits of rage where she attacks any other child and even pets, she is also seeing the psychologist and he is recommending she has an assessment, IQ test etc with thoughts of if she is on the spectrum, 2 nights ago she grabbed my daughter by the face and tried to twist her head around in a "snap the neck way" , she knew it was wrong and went and put herself to bed before I even went and found her, she then lied about it for 5minutes until telling the truth (my daughter has a habit of telling outright lies to get the others in trouble or won't admit that she did something first to the other child so I don't always know straight away what the truth is) my step daughter doesn't seem to show empathy or emotion unless it effects herself, she will hurt the dog because she thinks it's going to hurt the cat she and doesn't like dogs much but likes cats for example, on top of this my son (9) has developed anxiety and is not a good sleeper, my daughter (7) is such an emotional wreck, all she seems to do is yell and cry and stir up the other kids but then complain because she wants to be left alone and feels smothered. All 4 older kids fight and wrestle until it gets serious and they are trying to outright hurt each other, they compete constantly over everything, there is rarely a quite moment in my home, our youngest also has a health condition that he was born with and will always need monitoring, I've always suffered with depression but only once badly enough to need medication. Since having all the children I am now suffering badly with it and also developed bad anxiety to the point I was hospitalised in December because the panic attacks wouldn't stop for over a week, I couldn't sleep, couldn't eat, couldn't think, I liken it to a nervous breakdown.
My partner and I have been on and off "the rocks" due to the stress of it all. We agree on just about everything when it comes to the kids but he is a stick my head in the sand while someone else fixes it type of man, I'm a control freak (never was before) a dirty house now has me raging, I do not love being a mum anymore, I do not find joy in my children, I love them but I dread the time after school until bed time! All I do is yell and wish they could all be good. I know they aren't bad kids but together the 4 of them make life un bearable, I've done reward charts, they are rewarded/punished for good or bad behaviour, if I say something I stick to it, but not matter what if I'm not in the room with them they do what they want! No one is happy. Not a single person in the house! Hubby still works FIFO and when he is home he tries to compensate from not being here by being a hard arse on everyone and all he does is yell n put the kids down verbally, he used to be such a loving dad and when the kids would visit he would spend all the time outside riding bikes, playing in the garage, taking them to the park, watch movies, rolling around laughing with them, now it's all gone, I resent having to raise my step children because it's stopped me being the loving mother I was before to my 3 children, and yes I know that I married my partner they are a part of being with him I feel extreme guilt for feeling this way which makes my anxiety worse, I feel like I cannot continue like this, it's been TWO YEARS! I want to ask child protection to take them somewhere else but all I can think is its wrong. How can I do that to them? To my husband. But if I don't I think I will actually go crazy. What about my children? Don't they deserve a mum that laughs and plays with them? Who doesn't frown at them every time they come up to her and ask a question? Don't they deserve a happy home? I tried to leave my hubby in December because I felt he shouldn't have to choose to stay with his wife and other 3 children and send the other 2 away, that also added to my nervous breakdown because I just love him so much, he will not leave me either, we love each other deeply but our family life is making everyone miserable! It's toxic! If I do not have my step kids in my care here with me they will go to foster care, there is no family that will take them, child protection is involved due to the mother, but because I'm so "competent" and not a risk to the children we get no help. My family all work and have their own children and honestly it's hard for anyone to be around us now because it's so stressful for everyone/anyone to be around the kids when they are together.
I don't know what to do! How do you do the right thing when the right thing for each person is different?