About the quote where Isaac blesses Esau (really Jacob) to rule over his
brothers and his mother's sons. Laban called Jacob his brother in Gen. 29:15
because a brother can be any kind of a relative and the sons of his mother
could be sons or sons and grandsons, etc. You can't know if brothers are all
kinds of relatives and if sons include grandchildren, so the quote might be
too vague to prove that Rebeccah had other sons or if Isaac had other sons.