My own abuse was "amnesic" for about 25 years. I had panic attacks all my life, and the triggers where things that should have reminded me of the abuse. I know, my subconscious has the ability to block out memories as a defense mechanism, but at a sub conscious level I knew. This is not a belief or a I learned it somewhere, I know from experience this to be true. I also know a girl who abused who had similar experiences. I can tell you from personal experience that it is possible for them to have no conscious memory of it.
My own experience also says that the worse the abuse, the less likely they are to remember it, even through logic may tell you otherwise. One of the other kids the perps son was abused with me says he can’t remember. Yet when I warned him not to leave his kids with his dad, his response was: “i definately don't leave my kids with him.” Again, he has no memory of it, but knows.
While not a relative, My perps son has stopped talking to me all together. So yes, got the silent treatment.
“Your only limit within reason, is the one that you set up in your own mind.” Napoleon Hill, The Law of Success, 1925.