That sounds like parental alienation syndrome (or stepparental alienation syndrome), and it sucks. I don't live with my SO, but something similar happened to me with his son, 19. I was basically his mom for 2 years, he stayed at my house maybe half the time, never at his mom's. Then the court ordered "therapy" for him and his mom, and i went from hero to, if not zero, in the single digits lol. He is 19 now and i don't live there, so i just try to be polite and let it go. But it does hurt. Since you are married to their mom and have a lot more years with them it sounds like, i would recommend family therapy. Address these issues with a professional. If it could give my SO's son and his deadbeat cowbird of a mom a better relationship, it can probably help you, too. 

From what I see you have a couple of things going on. 

 1 the ages of the girls , I'm guessing almost teeens?

2. An ex/BF that tainted the water against life at your house and you being the scapegoat.  Also know as parent alienation syndrome (PAS) or pathological parenting. 
 

3. a wife who doesn't insist on respect for her spouse.  Does she let the skids get away with that disrespect with other adults or just you?    
 

4. a taste of legal consequences caused by lies from a couple of immature skids and that power has gone to their head.  
 

5 . you care more than their parents do.  

It hurts.  You go into steplife thinking you will at least be respected as the adult you are but that's not what happens.  The step parent (moms more than men ) becomes the target for all the negative energy.  What's worse is that you spouse thinks you should just take it because the skids....insert excuse. 
 

You have a wife problem. IMO. can she get a better shift so you don't have to suffer ? As for doing stuff for them, you can stop chasing them.  Provide food and water and safety while mom is at work but focus on your kids.  Mom can take care of the skids. That's her responsibility anyways.  Don't state it, just back off , be unavailable for anything to do with skids.  One of life's lessons is the learn you get what you give.  Treat people like crap and you get nothing in return.  Disengagement is to save us from hurt. From emotional trauma that only skids and a high conflict ex can dish out.  It's ok to put the parenting back into the parents.  
 

You have a wife problem. I know this because my SD33 shunned me for over 7 years while living with us full time. DH was a ball-less wonder and let me suffer. I constantly ruminated over what I could have possibly done to warrant being shunned in the home that I financially contribute to and do all the cleaning for. 

I got fed up and went to therapy. My counsellor told me to shun the bitch right back. He said that every time I "tried" by doing my "homework" as per my career coach, to "make contact three times a day," I was handing over all my power to SD to give her three opportunities a day to reject me yet again. I also had MAJOR abandonment and rejection issues from a horrific childhood and I was only opening myself up to further rejection "three times a day." Also, SD was heady on the power because silence is ascent and with DH not saying a word, SD's behaviour was being reinforced. She had us all by the balls. It's a total power move. 

Well, I shunned the cow right back. I also went ape-shit on DH and told him that him not having my back was a deal-breaker. Him allowing me to be treated like that at all, but especially in front of our DDstb23 was a deal-breaker. I did not want to model that kind of marriage in front of DD because you repeat what you know. I did not want DD to grow up and marry a man who treated her the way my DH allowed me to be treated. 

You have a MAJOR wife problem. Don't fall for gaslighting, "well, I can't make them like you," or "they're just introverts." I heard all of those. I stood strong and told DH that SD is not an introvert. She a bitch. It's insulting to introverts to use the word "introvert" as a euphemism for bitch. I also told DH about the Step-Mother's Bill of Rights in which one of the tenets is "I will not be treated like an interloper in my own house." DH knew he had to figure it out because I was done. My first attempt didn't involve me threatening to leave but I did use the term "deal-breaker," a couple of times and he got the mesage. 

You're going to have to address your wife and if you can't do it for yourself, do it for your bio. Picture her coming to you as an adult and telling you that she cried an ocean of tears from the agony of her husband allowing such an untenable experience for her. You can prevent that. 

I raised 4 SD and gave them everything and then when I had to move for my job and their dad began to have bulk time with them they quickly stopped liking my wife and me and moved to his side of the family and cut us completely out. It hurt me and my other children and of course, it hurt my wife. Now it has been a couple of months and we are all past it, but at the time it was incredibly difficult and confusing.

I have 1 SD that wants a relationship with us and continues to call us and spend time with her half-siblings.

This is a place to vent and I have vented my frustrations, but regardless of what they have done to me I still love them, wish them the best, and want things to eventually work out the right way. That is the key, I want it to work out the right way. I think it eventually will, but they need to figure things out for themselves and I have no problem giving that to them. 

With that said I want to offer encouragement to your situation. 

You said this:

I yelled up the stairs to her room and let her know I knew she did it, and that I wasn't happy. No profanity, no threats, no name calling. I certainly couldn't imply there would be punishment of any kind. That was one (and most egregious) of maybe 4 times in (at that point) 5 years I yelled at either of them when it was not necessary. I have been addressing my mental health for a while with proper treatment, but nobody's perfect

Do not blame yourself. As you said, nobody is perfect and there is not a person I know that has not yelled at their children. After my SDs left and cut us off I tried to figure out what I did wrong and eventually I realized I acted like a normal parent. I was always quick to apologize if I went too far, but I am not going to hang my head for common mistakes. I know I was a good Stepdad.

You are not wrong in believing you deserve more, but the problem with SKs is that they do not see you that way. I worked to earn their trust and it took about a year. I lost it when their dad became more involved when each turned 18. At that point, they were out of my house and I have 5 biological kids to raise so my focus shifted to them and only them. Those children do not have his influence and act much differently than they do.

Lastly, I draw the line at abuse accusations and this is something that you and your fiance need to have a real conversation about. I have been accused of abuse by three different SDs each time after they were 18 years old and they were living with their dad for a period of time. I was once accused of abuse by my oldest SD during an adoption home study so CPS did a full investigation on my family and found nothing and documented it. So the next time the abuse allegation flew CPS told them to pound salt. 

If you have already been accused of it, then you can bet you will be accused of it again. If you are going to continue with this then I would suggest getting an attorney on retainer and letting that attorney know when those girls are going to their fathers for a long visit. If the ex tries to pull this stuff again then your wife does not try to negotiate with him and he needs to take it right to her attorney and let them mediate it. I did this and it got the ex off my back and at least gave me peace until they turned 18 and were out of the house.

It really all comes down to what you want. If you want to stick it out with their mom then this is what you are in for and it will be a long road to gain their trust. Every time they see their dad you will probably have to start over or try and pick up lost ground. If you don't want that, then it is best to let your fiance know and move on. 

Good Luck

These things do not get better, over time, they get worse - if unchecked by the bio parent.

You could try some disengagement and only focus on your bios. You can have nanny cams in case of future abuse allegations. There are various tools in the arsenal to wage this step-war. Definitely get your spouse on the same page as you as to the need to address the abuse allegations.