There is probably some sort of negative correlation between those who get back to Charlemagne and those who are trying to authenticate linkages in the mid 1800s!
Your brother would be well advised to beware of Greeks bearing gifts! The Aussie has also conveniently overlooked the burial 20 years prior to his alleged marriage of the individual who links your Earls/Roberts to the line that goes back to Charlemagne - I think on reflection that you may access it earlier through the Earl/Turner link although this has a questionable connection (another, connected, Earl line also definitely links to that Charlemagne line though). The other problem with GeRe is that details of living people, including yours, which are included in trees can very easily turn up on websites accessible to the world - me and my kids ended up on an Aussie's tree. (I'm ever so slightly paranoid about my details being available to the world!!! I've met a victim of identity theft in the USA. Not an experience to be recommended.). I now never give details to anyone, no matter how much I trust them, which include living people.
But to return to reality:
neither you nor your brother appear to have traced the marriage of William born c 1828 to Ann, who John has implied may well have been Ann Bland.
In 1851
HO107/1753 folio 439A
Clifton Fields, Clifton
Absolom Foster head widower 72 tanner b Biggleswade
George Foster son marr 46 ag lab b Tempsford Beds
Sarah Foster dau in law 48 b Clifton
Grandchildren William 13; Daniel 10; Mary 7 all b Clifton
Harriett Foster dau unmarr 42 straw plaiter b Tempsford
Ann Bland Granddau unm 22 plaiter b Clifton
Ellen Sarah Bland grand dau 4 b Clifton
Absolom (which I believe was the middle name of your gt grandfather) also had another daughter Sarah who married Thomas Bland.
In 1851 William was shown as aged 20 born Shefford living with parents Thomas and Rebecca - he possibly added a year or two to his age when he married Ann to cover that he was younger than her.
There's a marriage in the June quarter 1852 in Biggleswade registration district where both William Earl and Ann Bland have reference Vol 3b page 582, so it's beginning to look fairly conclusive
The census progression also looks pretty convincing, linking Long Eaton to Clifton via Southill. What date aspect was troubling you?