Is there any way I can legally protect myself in my partner's custody case?

My fiance is currently going through a very nasty custody battle and has put in an application for shared residence to stop his x partner cutting contact with his children as and when she feels like it. Of course she has opposed it and gone for full residency and has since launched into a very nasty hate campaign against me as his partner. We live together along with my own ten-year-old son and had his children half the week, every week up until he applied for a shared residence, then his x started to cut contact amongst other things to try and make her case for full residency stronger. She is doing everything in her power to strenghthen her case and is using me as a tool to try and do this. We currently have contact cut and have not seen the children for a month because I am not allowed to have any contact with the kids and neither is my son. That makes it very difficult as we live together and neither of us want to end our relationship. But his x has stated that if he wants to resume contact with his children then either he has to move out or me and my son have to move out of our family home. Before we applied for a shared residence his x was happy for me to look after the children unsupervised as and when, but since the application is making me out to be unsuitable to be around her children. She refers to me as a child neglegtor and has called the police on me twice,the first time over a Facebook comment which was totally unrelated to her or anything to do with the case and then secondly for supposidley harrassing her, when all I have done is contact her when she has sent vile messages to me. I suppose what I want to know is, can she use me as a tool in her fight for full residency and can I legally protect myself from being used in court when I am not there to defend myself, because to be fair this shouldn't be about whether she likes me or not and is finding it hard to move on, it should be between my partner and her and the future of their kids, I shouldn't even be brought into the argument, but she is trying to bring me in at every point she can. The final hearing is at the end of this month and I am dreading it. Anybody who has any advice or suggestions on what will be the outcome of all this and if there is anything I can do to stop this from happening I would really appreciate it. Thanks