I really can't add much more to the wise words everyone else has said, but remember this: it does NOT matter one jot what "people" think if you leave an ill man. Being ill does not confer some sort of saint status upon sufferers ..... if they are bastards to start with, then they will simply be an ill bastard. Do you see what I mean ?
For those people you truly care about - close friends and relatives of yours, tell them the truth once you've split. Anyone who cares about you will be shocked and horrified at his duplicity, you will be believed and his "apparent" niceness in public (typical of anm abuser) will make what you say all the more shocking and make them want to help, care and protect you all the more.
Please please seek that legal advice ..... the Police, Social Services, the CAB, WomensAid, a solicitor ..... get as much information as you can. Forewarned is forearmed as they say. I know that your immediate instinct may be to leave yourself - and I can fully understand you wanting to do this, and indeed actually doing this if you fear for your safety - but as you own the house and he is a recorded violent abuser, I would seek advice about getting him and his revolting disgusting contemptuous brats out. I am not sure how/if this can be done ...... but it seems extraordinary that you - the victim - should have to leave your home.
Oh - I know it's easier said that done and from what you've written the vile pig won't go ...... but, I wonder, can the police/solicitor/courts not help you with an emergency injunction, which, when served, gives him x hours notice to get out ? And while this is going on, can you have a friend or relative to stay (even on the sofa) to ensure no repeated violence and/or damage to your property.
You absolutely do not deserve to live like this. The fact he has cancer is irrelevant. He may be entitled to be angry about this but if that is what behind his violence towards you that is no excuse. I would also say that he is emotionally abusing your child ..... to belittle him, put him down, ignore him etc is terribly damaging. Your child will probably also have picked up on your fear ... no matter how well you think you hide it.
You owe this disgusting excuse of a "man" no consideration, no obligation, and none to his nightmare children either. What you have done already for this nightmare brood and have put up with is already far above and beyond the call of duty.
Ok .... as you are married, no doubt you will face a claim for some of your property's equity. But increasingly, this is usually 50% (as a starting point for negotiation) of any equity increase since you married, not since you actually bought the property (if before). Please please get that advice - this situation is appalling.