In Flagg’s book I see two pages of information about the first couple of generations of Richard’s family. Much of the material is copied from Thomas Bellows Wyman’s Genealogies and Estates of Charlestown (see volume 2).
What I find interesting is that there is no reference to Simon Mellen, an alleged son of Richard’s. Wyman’s Genealogies include Simon in the entry for Richard, but he was basing his conclusion on the assumption that there was a direct familial relationship between the two. Many online trees contain a connection between the two, but I do not think that there is any factual evidence to say one way or the other. I have covered both families separately and together in separate places with extensive research into each. See Richard Mellen, a 3-Generation Study, and the Simon Mellen genealogy, for further information.
The only reason I included Simon in my coverage of Richard’s family was to make a point about the possibility they were related. My educated guess is still that they are not related as father and son. They may have been brothers or cousins, but we still do not know how.