Grane and Eyra Lopt are fictional characters from the two books about Eric thr Red by the danish author Preben Mørkbak: Here is book no. 1 in norwegian translation: https://books.google.no/books?id=R6ASCgAAQBAJ&dq=Eirik+Raude&am...
When people pulls the "show me reliable sources" I always answer: I bet you cannot even prove that your father is your father. If he is alive you can take a DNA test, but not even DNA tests can tell that 100%.
You can argue that birth records and church records for baptism is evidence, but they are not. They are only written facts of who the mother who gave the birth tells who the father of the child is. If the child was born in a hospital you cannot even be sure that the mother is correct. Errors happen.
Genealogy is about collecting as many facts as you find - with a certain level of certainty.
It does however stop for me when finding people from historical novels and TV series.
The book Remi points at has a clear text in the Foreword:
"This book is primarily a novel. But it is also an attempt to gather available knowledge about the Nordic settlement in Greenland, and especially about the man who founded a society which consisted of the late 900s and up to the early 1400s."
This means that you should read it as a novel, but if there are things you suspect is based on facts you should try to find them in real sources.
Remember: Things does not get more real by being printed in a book.