There is a really easy way of knowing if Anna is a heartfilia or not. I heard that there is a theme going on in that all the heartfilia's names are related to the beatles or something. Plus,let's think before making theories. What would be the point of Hisui being Anna's descendent? What would be the point of making Yukino her descendent? That would just complicate things needlessly.
Well,what I wonder is:will Natsu and Happy share what they learned or will they play ignorant? I am betting on the latter,and shaking my head in disbelief. For instance,Zeref stayed in sirious island and for some reason no one considered asking Mavis about it. Even if she played dumb,it would have been the obvious thing to do.