Sibling Estrangement

I called my father this past week. It was a short call, only about 10 minutes. That's how long our chats are. He usually fills up the call with the weather or politics or a current event. Rarely something personal.

So I was surprised when in the middle of the call he asked, "Have you heard from your sister?"
"No," I said.
"Yeah, neither have I."
I haven't heard from my sister since December 2013. She had always held resentment to me, seeing me as The Golden Child. She would vent to me about our parents, but if I validated and subsequently shared my own similar experience she'd lash out at me. The last talk we had was  a Skype chat. I tried to schedule another chat but that was it, she had other plans. I'll go it more detail with what she planned and how she carried it out, but it didn't work out.
"Did you try calling my sister?" I said.
"Oh no," my father said.
"Why do you think she wouldn't call you?" I said.
"Her husband never liked us," my father said, diverting the talk, "he would go in the other room to eat when we entered the room or not talk to us."
"Hmm, do you know why?"
"No I don't know why."
"Do you suspect why my sister doesn't call you now?"
"No, I have no idea."
I grew frustrated with his evasiveness. Maybe I was falling into his trap again.
"Maybe," I said, "just maybe, they are angry at you because your lawyer brought in the Adult Protective Services and they carried out an investigation which resulted in them receiving an ultimatum to leave your house and to have no further part of your care. Maybe she is still angry."
"Well I don't know about that," he said.
"What do you mean," I asked.
"Look," he said, "I don't remember. I was sick so my memory isn't what it was once."
"You don't remember this?"
"No."
Then he excused himself saying he had to go to dinner.
His conversations usually end abruptly with a breakfast, or a dinner or an ice cream social, anything to get out of actually talking.
He plays around with his memory problem. He had one seizure in October 2013 and said how he didn't remember what happened that week, gradually after that everything that I brought up that he found uncomfortable, then he brought up his memory as being at fault, unable to recall specific events particularly ones that had the most significance.
I'll like to go back and explore the events that lead up to the current sibling estrangement.