I've being there , done that.
I helped my Wife get coustdy of her children.
I think the best advice was given by "Corvin" and "jgnat" We went threw 12 court cases, in the first 6 cases he was supported by the John Abbort and the Black Shirts, a political anti-family court party.
Keep the religion out of it as much as possible, let her make the religion an issue, allways give the court the impression that you are just a parent who just wants quality time with his children, the mothers religion is no concern of yours.
And get a Lawyer, forget these signed personally signed papers, it should only take 1 or 2 cases. We used legal aide.
The WTS will only get involved if their interests are threntened (they call it "kingdom interests), if you try to stop your children from going to the KH during her access, so again, give the court the impression that you don't care where she takes them and she couldn't care if you don't take them to the KH during your access.
And keep a Diary. It will lower your own stress too.
all the best.