How do I convince my dad that he needs to put mom in a nursing home?

They promised each other years ago that they would take care of the other in case of illness at home. My Mother has been bedridden for many years and she is extremely obese. She has numerous health conditions that need diligent care for which he is not really capable of seeing to. She is verbally abusive to him. I suspect the abuse is also physical but he would never admit to it. He can't take care of her properly and his own health is declining. He just had a 2nd heart attack. I am afraid that she is going to literally put him in the grave from sheer aggravation and exhaustion. He is living in unsanitary conditions because he can't do all the personal care she needs and she will not allow anyone to come in to help her. It's disgusting at their house and I refuse to let my kids visit. I have tried calling social services and asking for home visits. They came out and offer personal services for her for which she takes for a short period and then tells them not to come back. I am at wit's end. My Dad says he will never forgive us if we force her in a nursing home but I love him too much to sit by and watch him die. What can I do?