I hear what you're saying about MIL and you have a right to be concerned about that - if necessary you can ask for an order stating that he not spent unsupervised time with her.
My kids don't spend unsupervised time with my mother and her stuff was just emotional and mind games.
But I just don't believe that you think your XW would abuse him. I really don't buy that. You've been married to her for years and she's never done anything to harm him. If she had, you would have left her and taken S5. You didn't.
You had a few grumbles over her mothering which I called you up on a few times because I thought you were being too harsh , and you've told me nothing to suggest you think she was abusing him.
When I asked you about your motivation for court before, you stated it was because you were afraid she would move away and not let you see him. I think this is the underlying factor here, that and anger/hurt at her OM and the RO.
From when you started to give up a little on your R, that's when this court stuff came in. You're more than welcome to disagree or think I'm rude, but I think this has more to do with you and XW than it has to do with S5.
As for letting her speak on the phone, Bruce is right. She could say you initiated conversation. When you speak, there is always the possibility of a row and then it will be your word against hers as to what was said, and you'd have no way to back yourself up in court if she chose to take you back there.
The best way to get out of tricky, potientially damaging convo's (and any are with this RO) is not to have those convos.
Also, you are still feeding her need by talking to her. You're not detaching properly. You need to let go completely to give her some incentive to come back to you.
