agree with post.
His GM left him money. You have this man's child her great-grandson. She would expect her GS to put a roof over his son's head. The house/money is not about punishing your X, it's about making ends meet, about living somewhere.
You need legal advice, and you DO need to get out of that relationship. he's hit you, he will hit you again, whenever the need arises.
Eventually your son may either experience violence at the hands of his father, or he will grow up to be just like him. You could end up in a situation where you give birth to your own abuser.
You can get a charge on the house so that if he sells, a proportion will have to be paid to you/his son. If he wants to raise the money to buy you out of the house, why shouldn't he?
You need to live, you can't stay with him.
Get legal advice, talk to the CAB, talk to your HV, your GP, and woman's aid.