You chose her to be the mother of your child and you wanted more children with her because you have complained that you wanted more than one and then she wouldn't allow it.
If she was as bad a mother as you seem to be suggesting, you would not have wanted a second child with her.
Re the porn movies - who DOESN'T have porn movies in their house? I've got one similar to lover's guide, if you consider that porn, which is stored in a wicker basket on a shelving unit in my front room, with all my home camcorder movies.
DD4 never touches this basket, nor would she without my permission. I have never watched the film in her presence, nor would I ever.
My only concern is that S5 knows about this, as he shouldn't do. Are you sure he was actually aware of these films?
It still sounds to me like you are getting bitter about this. You know how important mother-child bond is, especially in the early years of life. With your training you know that. You also know what it would do to him to be taken away from his mother when he is used to her primary care.
You were not 'documenting' her care of him before. Why now? I still think it is because you are losing the desire for an R with her. You thought you could reunite with S5 via her and now you are realising this won't happen, you want to change the residency.
Do you not think that if she knew you were documenting how she raises S5, she would not view this as more controlling behaviour? Because that's how I see it and you're not my husband.
I'm glad that you're not going to involve atty's - you would end up hurting everybody including yourself, but I am still struggling to see where this sudden shift in attitude towards her as a mother comes from.
I think primarily this is not about S5. This is about you, and these sorts of allegations, founded or unfounded, come up when there is a power struggle over a dying R and an innocent child.
It's the rough and tumble of modern divorce, and I really wish you would step back a bit.
I know you probably won't like my post. Maybe you'll think I've got a cheek. But that's how I see it.