I'm at my "wits end." My father in law refuses to listen and abide by the household rules. Since the death of my mother in law almost 4 years ago it has gotten worse. She use to do EVERYTHING for him. He has lived with us for 10 years. This is causing a strain on my marriage. We had an incident at home where I became very scared that there would be a fire. He used the microwave put two uncooked eggs in the microwave on a plate that is not for microwave use. I had put in cameras a week before this incident so I was able to catch the problem. He was told that he is not allowed to use the microwave anymore. He now knows that there are cameras watching him so now he "smirks" at the camera and uses the microwave anyway. This is just one incident out of many. He is combative, disruptive, disrespectful and at times obnoxious. What can I do? help!!!
Having said that, you are clearly burned out dealing with him.
It probably feels like your husband is choosing him over you or he would be gone if "He is combative, disruptive, disrespectful and at times obnoxious."
10 years is a long time. Your MIL being gone for four years has left you front and center with the problem. Is your husband able to take the lead on this? Is he willing? If he is able but not willing then perhaps you need to go on vacation and let husband put up with his dad. A 10 year old problem is not going to go away easily. Other things you can do is go for walks. Get therapy for you and your husband. Take a yoga class. You probably aren't using your best self to deal with this problem as you have put up with him for too long. I'm glad you came here to vent. If husband has deferred to you over the years, he may be ill equipped to deal with his dad but it seems like your FIL feels pretty secure in his acting out.
Come back and let us know how it goes. Give us more details about FIL health, husband's position etc, so we can better understand the situation.