My 3x GREAT GRANDFATHER SAMUEL SALTER'S 1848 WILL CREATES A HUGE MYSTERY?

SAMUEL SALTER b. 1779 TOPSHAM died. 1848 TOPSHAM
(married. 1802 LONDON JANE AYRES b. 1782)

The mystery here is that Samuel Salter's Will 1847 states his sons Robert and Easton Salter
plus JOHN SALTER BIROM SPURWAY "a child that I have nursed from his early infancy" to share equal parts of the Will.

John Salter Birom Spurway is my brick wall to find who he is son of.
I have searched for a birth record for John but to no avail.
1841 census Topsham shows the SALTER family including one year old John?
1851 census shows John age 12 years living with Robert Salter?
After this John doesn't show up anywhere.
The difficulty is which surname he is using?
SALTER, BIROM or SPURWAY.
SAMUEL SALTER employed SUSAN BIROM as a house keeper for several years.
Susan had a son JOHN MARTIN BIROM. (surgeon)
A theory yet to be proven is that mystery John might be John Birom's son hence the name BIROM?
Also HANNAH SALTER unmarried daughter of Samuel died July 1841 could she have been John's mother?
Both Hannah age (38) and John age (1 yr) were on the 1841 census.
The 1841 census rounded off years in most cases which stated Hannah as 30 years of age.
I have the death certificate which shows cause of death Stomach complaints.
Is it possible that HANNAH SALTER gave birth to John before her death in 1841 and died after childbirth?
This theory would explain John having the name of Salter?
Any help to whom baby JOHN SALTER BIROM SPURWAY belongs to is greatly appreciated.