Man train his wife to be submissive slut but theres still things she wont do...
One day her mother comes and while they all talk she just said how much she wants to be a grandma.
Later husband visits her mom and while they are alone he will said that he will breed her daughter but if she really wants that then she needs to help him - makes her daughter be more open minded about sex.
So next time when mom will talk with them will said something like it's natural for a women to give her body to a man she loves ( might use worlds like pussy etc. )
Wife after trainings will find the opportunity in this situation to fulfill her husband fantasy. She will try to convince her mother to watch how she and her husband makes out. When they will doin this in front of her mom husband somehow convinces her mother to watch them regularly. Each time will be more intense with new toys more humiliation etc. and when they reach a ''barrier'' something that daughter wont do mother will calm her and will said something like ''it's easy , if you love him you will simply do this but it looks like your love is not big enough''
Those worlds breaks her and now she simply lets her husband humiliate her the way he wants.
Somewhere mother forgot about the ''breeding''
Maybe mother at one point will be turned on ?
At one point mother wants the husband to give some love to other daughter she has. When she show him photo of her she will looks good but will be fat. He agrees but makes another deal - she needs accept that she will be humiliated due to obesity. Mother agrees and somehow managed it.
Husband wasn't easy on her. Made her cry, using toilet with open doors etc. BUT sex with him was a heaven for her even when he humiliates her in sex too.
He will lose weight due to hardcore sex with him and her sister. His former wife will be replaced by sister that lose weight and she will be the girl that will be pregnant with him.