Controlling, selfish, sarcastic stepfather. Any advice?

My husband and l lived with my mother for 12 months whilst our little house was being built. My mother had been a widow for many years. Eventually mum remarried. He appeared to be a good and jovial person whilst courting mum. Church wedding and reception followed. The man who left the reception showed his true personality..... Mr Hyde. We moved into our house, and consequently my mother and her spouse moved quite a long distance away... my family became isolated.... visiting occasionally, upon invitation. Stepfather detested my husband and barely spoke to my children (curt, abrupt, sarcastic, demeaning). I became a single parent, nothing altered... my children and l were not shown any kindness nor assistance.... we were to remain isolated from my mother. Recently, my mother died. My stepfather changed his tune and became Dr Jekyll from long ago, begging me to move into his house. My children and l felt pity/sorry for him (over the years he had alienated and driven all his friends away). In short, my family had spent in excess of forty years away from my mother and her husband, visiting upon invitation. Now that he was alone, he needed us to carry on performing my mother’s duties. He appeared to be a changed man. My family could not/ would not uproot their jobs to relate. Consequently he sold up his house and and purchased a property closer on our side of the city with the intention that we would move in together. The property is in his name jointly with me (my inheritance from my mother). Although we have not relocated permanently due to work location and school enrolment for the grandchildren... we keep in touch daily by telephone and visit each weekend for two days. Mr Hyde has returned. He is controlling, demanding, sarcastic..... some very unpleasant dirty habits have also come to light. Our family pay all outgoing expenses, utilities, insurance, etc. his contribution consists of $50 per week for himself and his cat. The new house has been completely furnished at my family’s expense. My son-in-law is an honourable man ..... he attends to all matters demanded by my stepfather regarding driving, chopping wood, digging, gardening. My daughter and l do the shopping, washing, cooking, cleaning... whatever requires doing. When we leave the house we must return at a certain time to make sure that his meals are prepared and set out on time. If not, he is belligerent, sarcastic and rude. We need to explain each action, any independent opinions and actions are met with great unpleasantness. His requirements must be followed to the letter. My grandchildren cannot be taken out on day trips without coming back to much stress, pouting and the usual sarcastic comments. In short, non of us want anything to do with him. Why did this situation arise? Because in our culture, the decent and humane responsibility lies with the young to take care of the old. These would have been my mother’s wishes. The man is quite old, in his nineties..... has selective hearing and difficulty in walking. Bragging constantly about the amount of work that he carries out.... yet, we cannot see what it is that he actually does apart from poisoning the lawns and cutting down magnificent trees..... a point of contention between us... we are unable to stop his actions when we are not there during week days. To quote him “...I am the Master and I will make all relevant decisions as it should be!” The final insult and pain is reserved for my son. My stepfather hates him with a vengeance.... has done so from the date of his birth.... my son is banned from the property. On the few occasions that we have travelled together, the situation has been extremely unpleasant. My son is ignored and not shown basic civility. Behind his back he is insulted and bitterly criticised. This behaviour causes great anguish and anger... bewilderment.... my son has not in any way throughout his life committed any act to earn such hostility. Our family is very close knit, we are best friends as well as family. In short, non of us wants anything to do with this bitter old man..... there is no one else to take care of his needs..... it is my duty! A nursing home or other such facility is out of the question.... he does not wish to interact with others.... and no one who has known him wishes to have anything to do with him. Yes, l have sought out counseling and our doctors advice.... without success.