I'm pretty sure his parents were John Folly & Sarah Seymour.
They married 28 March 1846 @ Chinnor.
John Folly(a chair
turner), son of John Folly(Transported).
Sarah Seymour, daughter of Peter Seymour(labourer).
Witnesses - Mary Folly & William Keen.
I cannot find a baptism in Chinnor or Oakley for your William Folly.
I did find a baptism in Chinnor, for John Folly, 17 Oct 1847,(Born 25 Aug 1847). Son of John & Sarah Folley,(Publican of Oakley).
I also noticed in the Index of Wills(Ancestry), William Foley left his fortune of £668-13 shillings, to Arthur John Medus, and Henry
Seymour Foley,(Ironmonger).

Steve.
From OxFHS - Chinnor Transcripts CD.