'Samuel Richardson' or 'Grandfather and Grandson with Greyhound and Hoop?'

While researching portraits of Samuel Richardson, I came across conflicting attributions of an oil painting by Mason Chamberlin. A copy of Chamberlin's 'Portrait of a Gentleman sitting at a table' in the Milwaukee Art Museum has been deemed a portrait of Samuel Richardson. The sitter bears a striking resemblance to other images Samuel Richardson, corresponds with the author's physical descriptions of himself, and the book in the sitter's hand has been identified as Edward Young's Night Thoughts, which Richardson printed -  thus it seems likely to conclude that this is indeed a portrait of the author.
BUT
Lane Fine Art has a portrait by Chamberlin of a man with a greyhound, young boy, and hoop, and the sitter in this painting is identical to Chamberlin's other portrait of Richardson. Unfortunately, the book is in his hand and the elephant folios behind him are unidentifiable. Lane Fine Art uses the single portrait of "Samuel Richardson", a copy of which is owned by Milwaukee Art Museum, as a comparative image, but Lane Fine Art identifies it as a 'Portrait of a Gentleman.' Richardson did not have any male heirs (so no obviously reason to have a young boy in Van Dyck dress), and there is no record of this painting in the catalogue of Samuel Richardson portraits. Lane Fine Art initially concluded that it was not a portrait of Samuel Richardson. However, when I came across these conflicting images online, I found that the characteristic light grey eyes left me with no doubt that this is Samuel Richardson and the likeness is especially striking when other portraits of Richardson are considered. After a discussion with Christopher Foley of Lane Fine Art, we have concluded that his portrait of the man with a greyhound, young boy, and hoop must be Samuel Richardson. The question remains - who is the young boy?

I am in the beginning stages of my investigation to find out more about this 'portrait' of Samuel Richardson. There are many leads to pursue - information about Chamberlin is scarce and sketchy - but by piecing together the little information on artist, together with Richardson's descendantss wills, contemporary reports of Richardson, and his large collection of letters, I have no doubt that this mystery will soon be solved.

Click on the links to find the images:  http://www.lanefineart.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=114&category_id=3&option=com_virtuemart&Itemid=1

and http://collection.mam.org/details.php?id=9144