This is quite an old post, so I hope you are still around.
If there are no parish records for their children, they may be found in the will of Daniel Pontifix/Pontifex, her brother.
There is a large chart of the descendants of John Pontifex. Link below, search for Pedigree of Pontifex.
A few lines down, middle of page, the daughter of William:
Sarah Pontifex, first marriage 14 November 1708, to John Devonshire of Burnham. Legacies to children of this marriage from D. Pontifex of Wooburn. This would be the will of Daniel Pontifix, of Wooburn, yeoman, 1725. This is available from the Centre for Buckinghamshire Studies. She also married James Style, son of James Style of Burnham.
Before John Pontifex of West Wycombe (will 1588/89), I have found some earlier Pontifexes in the Court of Common Pleas:
1551 Michaelmas/fronts a 944
Bucks. Thomas Tirry and Isabel his wife versus John Hawke, of Huchendon, smith; Christopher West, of Magna Marlow, husbandman; and John Pontifex of Huchendon, cook, on a plea of defamation. "Thomas Tirry and Isabel his wife have beaten, dispatched and killed one William Asshewell, their boy" or in the original: “Thomas Tirry & Isabell his wife have beton dispatched & kylled one Wyllyam Asshewell theyr boye”.
1552 Easter/fronts 363
Bucks. Thomas Wydmer, senior, versus John Pontifex, of Huchenden, cook; Richard Hawes, of Huchenden, husbandman; and Geoffrey Trye, of Huchenden, carpenter, on a plea of trespass: close at Hunchenden.
1553 Easter/dorses a 1481
Bucks. John Pontyfex and Joan his wife versus Geoffrey Trye, of Hydgyndon, carpenter, on a plea of trespass:close at Hydgyndon (Hughenden).
This John Pontifex of Hughenden, cook, and his wife Joan are probably the parents of John Pontifex of West Wycombe. The two parishes are adjacent.
Before this, there were some earlier Pontifexes in the Court of Common Pleas in East Claydon and Wingrave, going back to the 1460s.
https://books.familysearch.org/primo_library/libweb/action/search.do?vid=FHD_PUBLICPedigree of Pontifex
https://sites.google.com/site/meadfamilyhistory/home/legal-records/pontifex