As Joan says there does not seem to be any confirmation of the details given. The only reference I could find for a Robert Marshall born 1832, was his criminal conviction and eventual deportation in 1851. He was known as Marshall or Lockyer.
The only baptism I could find (not in Exeter) was a Robert Lockyer bapt 28.02.1831. in Cheldon illeg. son of Ann Lockyer. No trace of a Charles Marshall or Ann Lockyer being born 1810, nothing
on 1841 census. I went through Exeter prison records on 1851 census but could not find Robert Marshall/Lockyer. Sally

Can you tell us where you found details of this family? Cannot see a baptism for Robert Marshall or a marriage of Charles and Ann in Devon