Hi Paul
Nehemiah Halfords brother John Halford was my great x3 Grandfather.
Im in the same boat I think i found the father of them but im not 100% sure

On the 1841 census he is living in Blakeney Hill.

John Halford 40 Mason
Ann 35
Lois 13
Nehemiah 9
John 4
There is also a George Halford 11, but I don't know how he fits in yet.

All born in county.
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I have just had a look at the 1851 and George is a son (obviously missed him out of the running order on the 1841!) Nehemiah is a Stone Mason (Labourer) and they are still on Blakeney Hill. All born 'East Dean'.

John's d.o.b. around 1803 and there is this possible baptism on the FoD site:

Record_ID: 187269
Entry_Number: 21
Year: 1802
Month: Sep
Day: 19
Parents_Surname: HALFORD
Child_Forenames: John
Fathers_Forenames: John
Mothers_Forenames: Ann
Mothers_Surname:
Residence:
Occupation:
Officiating_Minister: Wm. Jones Curate
Event: Baptism
Memoranda: Son of
Notes:
Register_Reference: P209 IN 1/2
Page_Number: 74
Parish_Chapel: Lydney

A bit confusing as John jnr married an Ann and his parents look to be John & Ann also.

The following may be of help.
A search of Glos BMD Index at http://ww3.gloucestershire.gov.uk/bmd/MainMenu.aspx
for siblings of Nehemiah provides the following:
Child Surname Child Forename Father Surname Mother Surname Mother's Former Name Year District Office Register Entry
HALFORD Ann HALFORD HALFORD WILLETTS 1844 Forest of Dean Westbury on Severn, Newnham 5 350
HALFORD George HALFORD HALFORD WILLETT 1840 Forest of Dean Westbury on Severn, Newnham 2 421

This tells us that mother's maiden name was WILLETT(S). Sadly I cannot find a marriage in the registers but there is one for Anne Willetts in 1826 as follows:

Year: 1826
Month: Jul
Day: 27
Grooms_Surname: JENKINS
Grooms_Forenames: John
Grooms_Age: [not stated]
Groom_Condition: Bachelor
Grooms_Occupation: [not stated]
Grooms_Residence: Forest of Dean
Grooms_Fathers_Surname: [not stated]
Grooms_Fathers_Forenames: [not stated]
Grooms_Fathers_Occupation: [not stated]
Brides_Surname: WILLETS
Brides_Forenames: Anne
Brides_Age: [not stated]
Brides_Condition: Spinster
Brides_Occupation: [not stated]
Brides_Residence: Forest of Dean
Brides_Fathers_Surname: [not stated]
Brides_Fathers_Forenames: [not stated]
Brides_Fathers_Occupation: [not stated]
Licence_or_Banns: Banns
Date_of_Banns:
Signature_or_Mark: He signs she marks
Witness_1: Mark of Amy Jellamy
Witness_2: Mark Henry Hawkins
Other_Witnesses: Charles Fennell
Officiating_Minister: Charles P. N. Wilton Officiating Minister
Event: Marriage
Memoranda:
Notes:
Register_Reference: P30 IN 1/5
Page_Number: 50
Parish_Chapel: Awre

Time and place look good and there are 2 baptisms for Ann(e) Willetts in Awre - first one in 1804 and the second in 1807.
A search for a baptism for John Jenkins produces this entry:
Year: 1802
Month: Feb
Day: 7
Parents_Surname: JENKINS
Child_Forenames: John Halford
Fathers_Forenames: [not stated]
Mothers_Forenames: Nancy
Mothers_Surname:
Residence:
Occupation:
Officiating_Minister: Charles Sandiford Vicar
Event: Baptism
Memoranda: [1]base S[on] [2]b[or]n Nov[embe]r 9 1801
Notes: Blakeney Chapel
Register_Reference: P30 1 IN 1 Part 2
Page_Number: 485
Parish_Chapel: Awre

This would appear to be the father of Nehemiah.

Best wishes
Mike