My friend has recently split with her DH, and they have had mediation which apparently is a prerequisite of getting divorced. They should get their decree nisi in the next month.
My friend takes home £1300 a month and was previously the breadwinner in the family with her DH working p/t and doing the bulk of the childcare.
Her DH wanted to have DS live with him, but upon splitting, they have agreed to have 50/50 care, and DS currently spends 3 nights a week with dad and 4 nights a week with mum (my friend).
During mediation, friend and her stbxh agreed in writing that her stbxh is the main childcarer. On this basis, stbxh claims the CB, CTC, WTC, and works p/t, so also claims some HB too.
My friend lives with her parents at the moment, so stbxh can remain in the council house they previously lived in together.
Friend wants to privately rent somewhere for herself and her DS, and has discovered that to do so, she will probably need to claim HB, since private rents are quite high and she couldn't afford this on her wage alone.
She mentioned to her stbxh that she was considering privately renting and he has become very angry about this. He has told her that she wont get housing benefit at all, because officially she does not have a child living with her, and she can't claim to have a child living with her because that would affect his entitlement to CTC,CB,WTC,HB and apparently he can't afford to live without the extra money, and now he is being nasty, calling her a shit mother because she doesn't take her DS out every day (she works full time) and she relys on her parents to take DS to school in the morning. They have sometimes dropped DS at the school gate and not walked him into the classroom so stbxh is ringing her saying what a shit mother she is.
stbxh has also started telling DS she is a crap mother, and has told my friend that as soon as DS is 7, DS will decide where he wants to live and he is hoping DS says with him.
Now, her stbxh has told her to start paying child maintenance (because of course she can afford all of this
) because if she doesn't pay him, he will go to the CSA.
(He has threatened this for a long time)
I spoke to stbxh to try to calm the situation down, (friend asked me to) and stbxh ranted on at what a shit mother she is, and that he wont apply to CSA, because all he has to say he is a main childcarer is a written agreement drawn up by a mediator and signed by my friend and her stbxh. They have not been to court at all and stbxh is worried that if she claims she is the main childcarer, he will lose all of the benefits and wont be able to survive, but he wants as much as he can get out of her (his words) and he enjoys pissing her off. He told me it's a man thing. 
stbxh has told my friend that access is no longer dealt with in court, but only in mediation now. 
Now my friend is all confused and doesn't know where she stands or how much the agreement in mediation would stand up in court.
Personally, I have always found her stbxh a complete control freak, who admitted he doesn't enjoy working, bled my friend dry while they were living together but begrudged her anything. He is one of lifes takers imo and has said lots of times that he is a superior parent to her, because she is a woman
He constantly claims men are superior to women and makes sexist remarks in every conversation, or jokes at a womans expense, enjoys telling women what their role is in family life (to look after the man and give him BJ's yuk)
One of the reasons they split is because stbxh would scream at my friend if she tried to discipline her DS, and stbxh would send them both to different rooms as if they were both children, before screaming at my friend 'Who do you think you are, telling him to do XYZ...you can't tell him that FFS'
Basically, her stbxh believes there is only one way to parent, and that is obviously his way, down to the food DS eats, the drinks he drinks, the places he goes etc etc. He's like an army sergeant.
Any advice or opinions on how to deal with a man like this? Or how binding a mediation agreement is? Or what my friend should do now?
What are the courts likely to make of this? stbxh says my friend will be seen as a shit mother if it ever went to court because she wasn't there for DS 24/7. (She was at work trying to pay for everything while stbxh worked 4 evenings a week p/t)
My friend is desperately trying to keep things amicable, but is finding it harder and harder and is hoping the bitterness will soon settle down. What are the chances??