Your information seems to match my uncle's family tree almost exactly.
He also has George Glew (who was married to Mary Ann Sykes) as being the son of John Glew and Sarah ?, though with a differnet death date of 1875.In all he lists 14 (!) children.In addition to George (1831-1899/1900?), he lists William (1819-22); John (1823-25); Richard (1825-25); John (1825-45); Sarah Ann (1827-?); William Augustus (1829-59); Johnson (1833-?); Catherine (1834-?); Joseph (1836-?); Jane (1837-57); Susannah (1839- ?); Mary (1842-74); and Aaron (1844-75).Sarah Saunderson sounds like a strong possibility as their mother's surname.
John Glew is also listed as having 3 siblings: Kitty (1788-?); William (1789-?) who married a Sarah ? (1801-54) [incidentally there is a memorial plaque to Sarah in Althorpe church, Lincolnshire]; and Joseph (1806-?).
Like you my uncle listed John Glew as the son of John Glew (1762-1805) and Jane Johnson listing their marriage as 4 Dec 1787.He also notes that he was a farmer and is buried in Althorpe churchyard.
He then lists this John Glew as the son of Nevil Glew and Elizabeth Plumtree, both of Althorpe, who were married on 19 Oct 1758).
He tentatively posits Richard Glew of Keadby (1709-90) and Mary ? (1698-1782) as the parents of Nevil Glew.Again there is a stone to Richard Glew in Althorpe churchyard, though Althorpe Register lists Richard's death as 24 July 1789.
There's nothing beyond that, so there's still some work to do both backwards and forwards in time.
Funnily enough, we were In Wales on holiday a couple of weeks ago and passed through Swansea!Thanks for the information about John Henry Glew's wives and that their father once ran a pub in Manchester.My parents used to run a pub in Beverley.I am sure that a lot of the Glews come from the Althrope region of Lincolnshire (see my posting re: the origin of the name).