Good evening Anne, Do you not find it amusing and somewhat annoying when you think the person with whom you regarded as your grandparent all your life, only to find out that the lady in question is not your grandmother. I too had a grandmother called Catherine Thompson, only to find she isn't, she was still related though through the paternal line. So you too have a Hynan in your clan, did your Thompsons stay put or did they moved across Ireland or move further afield 'across the pond'???
Kind regards Sharon.