The substance of this post is purely conjecture which I generally try to avoid altogether, but here goes:
25 January 1806 John Backhous of Grays Inn Road in the County of Middlesex Brass Founder will proved at London. John Backhous's will had substantial bequests to John Backhous otherwise Harcourt and Ann Backhous otherwise Harcourt natural or reputed son and daughter.
Source: London Metropolitan Archives and Guildhall Library Manuscripts Section, Clerkenwell, London, England; Reference Number: DL/C/438; Will Number: 133
21 July 1827 Abraham Harcourt of 35 Great Sutton Street Clerkenwell Brass Founder will proved at London.
Reference: TNA PROB 11/1728/314