Your dad sounds similar to my mom as far as not letting others know about things. The only reason I find things out is because my grandmother tells me things.
Recently I found out my grandfather died(about a month ago). My grandmother told me; my mom still hasn't said anything. I had never met him and my mom didn't have a relationship with him, but I had always wished to have had met him.
Unfortunately, it sounds like this is how your dad deals with things. Ignorance is bliss. As much as we don't like it, we really can't change that.
Regarding your stepmother, it's probably best to leave it as is.