My question involves a marriage in the state of: CA

My marriage is 18 years old and we have had trouble from the start due to his family. We have an autistic son. Two years ago, behind my back, he took our son to see his sister and his distant cousin. This wouldn't have been so bad (aside from the fact that his family hates me) had it not been for the fact that cousin also has a non-verbal and severely autistic son who has never communicated until the cousin began to use a method called Rapid Prompted Method (RPM) with him. Using this method (a form of Facilitated Communication that has been used in the past to falsely accuse parents or caregivers of abuse), around 2014, this woman (his cousin) accused her son's physical trainer (with whom she had had a falling out just a week ago) of sexually assaulting not just her son but also 7 other kids (the other parents denied that this had ever happened). I learned of this through a mutual acquaintance and we stopped talking. The criminal case against the trainer was dismissed and the woman was warned against wasting the Court's time in the future.

Thanks to his meddling sister (who was aware of this incident and who knew I also disliked the cousin), in 2017, a meeting was arranged by my STBX SIL for MY son to "have an RPM session" with the cousin. I was told the kids were visiting their aunt and my daughter later revealed that they had also met Aunt X (the cousin) at my SIL's house. Apparently, at this meeting I was dissed as an awful, awful mother and that she (cousin) had wanted to call CPS on me for a long time (note that this woman has never been to our house and we had only talked for a few months before I heard what had happened and cut the woman off). I was infuriated and told my husband about the criminal case (that he claims he did not know about - likely a lie) and we have been in a bitter marriage since.

The other thing is that - post divorce - he could establish contact with her (at his sister's encouragement) and I do not trust him any more. I fully expect this woman to spring abuse claims against me after using RPM with my son and I do not want her (or his sister) anywhere near my son.

1. My first question is if I can get a restraining order against her and his sister to prevent them from having access to my son now (and after the divorce) ?

2. Despite everything, I do not believe that he is a bad father but he gets influenced by his sister, so I do not want to go for full custody. Is there any way custody agreement can be written up so that that I can prevent my STBX SIL or his hag cousin from having access to my kids (especially my son) after the divorce ? Especially, if I won't be able to get a restraining order against them ?

Post divorce, I want to avoid future fake RPM sessions for both my children's and my own protection. If preventing SIL's and Hag's access via custody agreement is not possible, is sole and full custody (at least of my autistic son) the only option and would I be able to get it if the Court was made aware of the cousin's chequered background ?

Please advice.