I hope the "Payne Researchers" are still monitoring this line of queries.

I am married to a John Payne in New Zealand. A Common Name from what I can see.
He comes from the following Essex Payne Family:
John Payne 1963 NZ /
George Wilfred Payne 1933 NZ /
Thomas Payne 1876 Taulau, Durham m in NZ /
John Sidney or Sydney Payne 1854 Copford, Essex m Ann Elizabeth Cuthbert/
George Payne 1821 Gr Coggeshall, Essex m Sarah Brown /
George Payne 1799 Icklgham, Suffolk, England m Lucy Smith /
So my query is, does anyone have access to Essex Parish lists / actual documents please who could source / get copies of the birth details or baptism details for
John Sidney or Sydney Payne 1851 Copford, Essex.
He was baptised on the same day as two other Payne's - William Henry (his confirmed brother b1851)) and Sarah (possibly a sister b1851) on 23rd June 1851 @ Kelvedon, Essex.
There is an older confirmed sister Mary Ann (b1849).
Mary Ann PAYNE’s birth was registered Dec Q 1849 ie probably born Oct - Dec 1849
William Henry PAYNE’s birth was registered Jun Q 1851 ie probably born Apr –Jun 1851
Doing the gestational maths:
The latest birth date for William is Jun 1851, which gives a conception date of abt Oct 1850.
The earliest birth date for Mary Ann is Oct 1849
So if John Sidney PAYNE is Sarah & George's child, he must have been conceived after Oct 1849 & born before Oct 1850.
That only gives a birth window of the months of Jun – Oct 1850 ....... But he does not appear to be in the GRO – not for Essex or Suffolk – not under John, unnamed male or Sidney/Sydney - not PAYNE, PAINE or PAIN
In the Apr 1851 census John is aged 1. So if he is George & Sarah's son he was probably born in Jun Q 1850
And then one asks ... Does the fact that John Sydney was baptised with the younger William somehow relate to all this?
My theory is that he could be the illegitimate son of some family member or acquaintance, that he was born 1849-1850 and that George & Sarah fostered/adopted him.
Or that his mother was a very busy pregnant woman!
Any ideas will be greatly appreciated
Thanks
Gaye