Just read your question re John Austin ... I have just come across the same anomaly in my research!
On my Mother's Grandfather's side of the family, I have 'documented' links to Matthew Austin b 1562, and I am happy with the research back to a Henry Austen b 1330.
However, I am unsure about John Austen (of Wingham, Kent) being married to a 'posh' lady, Isabel Willoughby (of Woollaton, Notts). This does not seem likely, given the class and geographical divide!
Most sources have Isabel married to a Philip Boteler (of Wootton Woodhall, which I believe was a manor house in Watton by Stone, Herts). However, Geni sugggests that this was a second marriage or that Austen was Isabel's maiden name, which excludes her being a Willougby. Also, there seems to be a link provided in Family Search, Pedigree Resource Files, in three separate names, all of which have John married to Isabel Willoughby, although they may all have copied one of the others!
All very sad, because if it was Isabel Willougby then via links with the Freville family take us back to Henry 1 and William the Conqeror.
The only way of positively disproving the marriage would be if there was a definitive record of John marrying a different Isabel.
Not sure this helps, but I would be interested in where you are in the Austen family tree. I get there via, Hawkins, Hubbard, Curtis, Lewis and Henry Nash who married Mary Austen b 1688.