I would suggest the book is clear Thomas Spring on the right with the number 13 in a circle is the son of John Spring (mother unknown)
However the author is not sure if the two men John Spring and Henry Spring are brothers to William Spring b. circa 1730 & Thomas Spring b. after 1733 or are sons of William & Thomas (or even sons of William or Thomas).
The numbers in the circles refer to further information about the person named it is their database number.
Are their any contact details for the authors William & Jane Spring, they might now (17 years later have more information)?
Cheers
Guy