Seems strange writing this so long after you posted your message!
I have a tentative connection to your family through George Allum and Sarah Wade.George and Sarah married in All Saints, Great Marlow, Buckinghamshire on 11 July 1779. Witnesses at the wedding included Ann Wade (sis?), William Allum (pos fa or bro), and Ambrose Shaw.
Ambrose Shaw went on to marry Mary Allum in 1785.
I believe the witness, William Allum, to be either my g.g.g. grandfather or my g.g.g. uncle.He is a witness at James Allum's (g.g. grandfather) wedding (1821) in Great Marlow.I think your George Allum may be James's uncle and perhaps brother of William. They are almost certainly all related. If you have more details I would love to know them and more than willing to share what I have.
I think the Allums were fairly recent immigrants into Great Marlow and that James, William, and George may have come from elsewhere in Buckinghamshire or Berkshire.There are lots of Allums in Langley Marish, Buckinghamshire for example.So far I have not been able to make a connection.