Pure speculation - you need to get some certs to firm this all up
But
this could be the missing William in 1841 (ie son of 'old' William who was married to catherine, father og John bn 1846ish, died 1848ish)
HO107 326 13
Church Lane Writtle
William 25 Ag Lab Y
Sarah 25 Y
George 4
Clara 4mths
MArriage
Jul/Aug/Sep 1840
Chelmsford
William Brazier
brides on page Sarah Bonnington, Sarah Juniper, MAry Rayment, Hannah Westwood
so a choice of two Sarahs
John's birth cert should give mums maiden name, and help confirm all this
