If I write about my dad finally revealing what happened to him during the war, is it a memoir?

My thought is that if I tie myself into it as in; One chapter talking about his experience, the next my experience growing up that relates to his experience and so forth, it is still MY story.

Or is it then HIS story? If so, then what category does it fall into?

I'm confused. I've started and stopped on this several times and I think that this is at the core of my problem.