Controlling Mother

My father 57 remarried 3 years after my mother died, my new stepmother 40 was nice to me 24 and she had a daughter 18. Then my father had an accident, he survived but was left in a wheelchair and had some brain damage. As he hadn't updated his will since marrying, she wasn't in it. but it wasn't a big deal as she only just had to make a claim against the estate if he died. I was studying law at the time, but my stepmother wasn't concerned about herself it was her daughter, before his accident her and my father were going make it official and adopt each other child. That was stopped because my father wasn't now legally competent to sign any papers. After doing some thinking my stepmother decided to marry her daughter to me. If not my adopted sister than being my wife was the next best thing. I did date and wasn't in a current relationship and I was quite shocked when she told me she wanted me to marry her daughter. Her daughter is quite attractive takes after her mother. But I didn't think would want to marry me, but she was dominated by her mother all her life. So, she would do as told and the prospect of regular sex with a wife appealed to me, so I agreed. A quick marriage later and a couple of months after our wedding she was pregnant. A couple more months, sex stopped as her mother said to stop till after the birth of our son. I thought we could go a bit longer, but her mother would know best. But it didn't end my getting sex, as her mother took it upon herself to drain my balls during lean period as I had started to call it. The mother was good at draining my balls and I got her pregnant. She hadn't taken precautions because she assumed she was past it as her and my father had tried and failed. Not thinking it might be him not her, but the deed was done. My father had major surgery that might help him, he died on the operating table due to reaction to the anesthetic. That was last month, my wife is eight months pregnant, and her mother is 4 months pregnant. Both sleep with me and only her mother has sex with me, and I should back fucking my wife by the time her mother stops sex with me.