Hi Hazel,
          Sorry i dont have Longcot, Sparshot or Childrey PRs but did search surrounding villages
but came up with nothing im afraid. 

Martha Maddons/Maddoms i couldn't find her baptism either. I searched Steventon as this was 
where they married also Abingdon and all nearby viillages with no luck 

Ok i did find this from Charney Bassett PRs
    Baptisms
Jan 14 1756 Robert Roby son of Robert and Anamaria ( incase you didn't have it )
    Children of Robert and Martha ( name spelt Roby and Robey ) 
Oct 15 1780 William
Aug 31 1788 Anna Maria
May 23 1790 Mary
Jan 27 1793 Giles 
Jan 25 1795 Martha
  Other children it says parents Stephen and Martha 

  Also why such a big gap between William
  and Anna Maria 

 I then searched Burials and found the following
 Sep18 Martha Roby age 64
 Jun 3 1828 Robert Roby age 72
 Nov 13 1839 Martha Robey age 72
 Oct 6 1841 Stephen Roby age 80
 I went back and searched again and found Stephen was Roberts brother.
I can give you details of Roberts brothers and sisters if needed 

 Let me know your thoughts on this please 

                           Sue