As you say, the first evidence of another generation is the time span from Jonathan Pinkham, b. 1684 to Christopher, b. 1735. Since Hannah Brown, Jonathan's first wife by whom he had all his children died in 1731, we immediately have a problem. Jonathan himself died in 1735, the year of Christopher's death.
As Martin Hollick has pointed out many times on this forum, the Sinnett book has many errors and should be suspect.
As a start, on page 746 of Alexander Starbuck's History of Nantucket we find among the children of Richard Folger "Ruth, born 30th 1 mo. 1732: married Christopher Pinkham son of John".
Some of my data is from correspondence with a genealogist that spent time with the Quaker records, but I can also refer you to the work of Robert St-Gelais on the net. You can go to the data on John by going to the URL: http://www.my-ged.com/db/page/stgelais/70594http://www.my-ged.com/db/page/stgelais/70594.
As you will discover, the data you have for Abigail Bunker, wife of Shubael (note spelling) is entirely correct. Abigail, the wife of John, is one of the other myriad Abigail Bunkers of Nantucket, b. 13 Jan 1713, Nantucket, d.18 Jun 1799. Her parents were Jonathan Bunker and Elizabeth Coffin.