What are the chances that I will get the full custody?

I am now married with my wife and had a newly born daughter and also have two kids with my ex-fiancee. My ex-fiancee and I had agreed with the court to have a 50-50 child custody with my two kids and I am currently paying and agreed to pay child support for them. We also agreed to have the two kids to spend the week with me or with her every other week. During the course of our relationship, we filed a domestic partnership just to cover her and my 2 kids with my current benefits with my present employer particularly with medical and dental insurance as my primary beneficiaries. When my ex-fiancee and I separated in 2005, I immediately filed and updated my insurance beneficiaries to remove her (my ex-fiancee) as my dependent and leave my 2 kids as my primary beneficiaries. In 2007, I met my wife and immediately got married. I filed and updated my insurance benefits and added my wife and my two kids (with my ex-fiancee) as my primary beneficiaries. Recently, my wife needed to see an eye doctor and she was denied to use my benefits and according to them, somebody already used it. I checked with the insurance company and found out that my ex-fiancee used my vision benefits without my consent. I checked with my employer said that they already removed my ex-fiancee and updated my file, but the insurance company said that they haven't updated their file and my ex-fiancee is still covered. I called my ex-fiancee and asked her why she used my benefits without any permission or consent from me and told her that she should not have used it since we are no longer together and our domestic partnership agreement with my employer had been waived when we got separated. She told me that it was not her fault that the insurance company had accepted her claim. Now, I am filing a complaint against my ex-fiancee for using my benefits without my consent. There were also instances that my ex-fiancee ask favor from me to have the kids spend the week with me which is not supposed to be my scheduled week with me and she left on a vacation with her current boyfriend. Now, I planning to file a full custody with my kids with her because I found out that she is unfit to be a mother and a parent. While the kids are scheduled to be with her, she always leave the kids with her mom and spent more time with her boyfriend than with her kids especially on special occasions. Also, she always use the court or filing a case against me just to harass me at work and at home when she needs something. I am already stressing out, mentally and physically of her threats to bring some issues and wanted to modify what had been agreed upon with the court. With these issues with her, can I file a case against her and file a full custody with my two kids? What are the chances that I may get the full custody with my kids? Do I have a case against her for using my benefits without my consent?
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For the benefits, you can sue her in a civil court for the amount the benefit covered, but it has nothing to do with the family court suit. For harassement, it is very difficult to prove it. If she has a viable claim in the suits she's filing against you, then the court will find it perfectly reasonable that they be served to you at work. In order for the 50-50 arrangement to be modified, there is going to have to be something more substantially that just her leaving the kids with her mother to spend time with the boyfriend. Generally, that is just not enough for the court to void a compromised on agreement. It looks like you're out of luck. Sorry.
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