Fiction and lies or is it truer that way?

So, when deciding how to write about my grandmothers, I realized there was a lot I didn't know. I was about to research and find out some information, but could not know their internal spaces. So, I made a decision to speak as them, in the first person, which instantly made what could have been considered non-fiction into fiction. Or did it? There is now something called speculative non-fiction, which can include what I chose to do. An excellent book that discusses the blur between fiction and non-fiction is David Shields' Reality Hunger. I highly recommend giving this a look-see if you are working on the edge of memoir-biography-fiction, which according to him we all are all the time anyway, since so much of memory is fictional anyway and family stories are just those: stories ... What do you think?