Apologies for being late to this question. I have a Thomas de Stafford Buckingham (born Ashwater about 1520) as a greatx13 grandfather, he is also related to me in other ways through cousin marriages but that another story. I believe he had more than one marriage himself but the one I am descended from is his marriage Lady Mary Chaunter (b.1522 Ashwater) and their son Thomas Buckingham (b.1545). It is possible that your John Thomas Buckingham was his brother (born two years earlier). It is said that Lady Mary Chaunter's father was Edward Stafford, 3rd Duke of Buckingham (executed for treason in 1521) and she was born after his death. Alternatively I've also been told that this is incorrect and he was actually her spouse's father, very confusing. The evidence is all rather hazy and family tree sites are littered with some very odd/dodgy trees with little or no evidence. You will note I am not a Buckingham but my Paternal grandmother was Thirza Buckingham of Twitchen. My late father did much of the family history research into his Mother's family back in the 1980s and 1990s, well before anything was online. Do get in touch and let me know if you've come across anything else since you posted your question.