Custody Questions

My ex and I have joint custody. He has had our child for the past month since CPS was involved with our family. We have finally received a diagnosis from a doctor which should drop the investigation. My ex husband has informed me that he is now taking me to court. I have found out recently that my ex husbands wife has been stalking me on Facebook and friending everyone she can. Recently I found she friended my husands sister who disowned my husband and our children because of my disabled son. My question is can whatever my husbands sister says about us be used against us in court if she were to testify? I know she doesnt like me and wants me and my children out of the picture so who knows what she is telling my ex husbands wife.
My ex husband and his wife have tried to run me out of the picture. My ex husband was adament that he did not want my daughter in girl scouts. Well, a few months later, as my husband and I were taking my step son to sign him up for boy scouts, there his wife sits signing my daughter up for girl scouts. Not to mention, my husband never works with my daughter on her homework. His wife signs everything for her school. She makes my husband leave my daughters soccer games to take her son to his games. Now to find that she is stalking my life on top of everything else.
Can whatever she is trying to dig up on FB against me be used against me?

The question is whether he will be able to get the information he finds on facebook into evidence. He may need additional parties present to testify to authenticate the documents, pictures, etc. If the material is relevant to the custody case, then yes, he should be able to present the evidence to the court.