My Mom's angry at me and won't let me see Dad. What do I do?

My parents are both 92 and live in their home independently. My Dad suffers from dementia. He is terrified of her as she emotionally abuses him if he goes against her wishes. He wants to see me, but I don't have any access to him. She does not allow him out of the house and won't let me in the house. He is a prisoner there. She doesn't talk to him if he tries to do anything that she hasn't approved. I want to see my father, especially because of his advanced age. I'm afraid she won't let me see him if he goes to the hospital or when he is dying. I spoke to APS, but they said that they can't "see" the kind of abuse I'm describing, so they can't do anything. Do I have any rights in this situation? He is under her control and is powerless.