I predict that Gwen’s Grandfather is invisible and staying at home but no one knows that he is staying at home. I think this because he called and left home for a while because he had to get away for a while, but sense it is the sequel of Things Not Seen where someone else was invisible that Grandpa it too. I think he is staying at home because why would someone leave on no notice at all? I also think this because if you were telling someone that you were gone then why would you call and leave it on an answering machine? That is my prediction.