Is it wrong or could it be used aganist you to write a magstritate a letter?

I have been going through a custody battle for almost 2 years now...my ex is doing things to me, my fiancee and my children..most of it is emotional crap...one week to keep my kids from me he reported to children services that my fiancee is abusing our two kids...well that was going to be closed...the following week he went a little to far and is now accusing my fiancee of ually abusing our 3 year old daughter...he is going to put this little girl thru some terrible tests just to keep my kids from me. I know my fiancee I am with now and he would NEVER hurt my kids that way. As a matter of fact w/my daughter when I was working he would never change her diaper he would ask one of our neighbors (both female) to do it. Well we are at our wits end...we don't know what to do...who to talk to...my fiancee even called the police on himself...he said if he is going to make this false allegations aganist him he wanted to be arrested...so I wrote the magistrate...but I haven't mailed it yet