Date of Birth given as 1861 on marriage certificate when he said he was 21 in 1882. Date of Birth given as 1864 in 1901 census and 1862 in the 1911 census. 

Date of death given as 12th Feb on gravestone but 17th Feb in Coleraine Chronicle death notice!! Buried in the old graveyard of Englishtown Presbyterian Church (between Coleraine and Garvagh, 4 miles from Coleraine), along with wife Ann Brewster, daughter Tilly, Tilly's husband George Neilly and "twin son died in infancy".

Registration number    Forename of deceased    Surname of deceased    Date of death    Age at death    Date of birth    Sex of deceased    Registration district    
D/1947/94/1008/34/137    William    Gray    17th February 1947    86        Male    Coleraine(pre-1973 Q4)
Of Mountsandel Road (Tilly's home), son W J Gray PAD.

According to Coleraine Chronicle Obituary, she was 97 (= DoB of 1848) but this does not tie in with age given when married. The marriage certificate gives her as aged 28 when she got married on 16th March 1882 (= DoB of 1854). This would make her born in 1854 whereas the obituary makes her born in 1848. The 1901 census gives her as 47 so she was born in 1854 according to it!!  By 1911 her age is 60 (= DoB of 1851)!!  This one ought to be correct as it makes her 11 years older than the age her husband gives in the 1911 census (so she is no longer hiding the age difference, AND, she may well be wishing to claim the OAP and therefore needs to give her real age.  It is also a sort of average of the ages she gives.

Died at "Dun-Da-Bhann", Mountsandel, Coleraine - daughter Tilly's home. 

Date of Birth = Macosquin Presbyterian Church Births Register.  She was baptised on 13th January 1884 by a neighbour, the 24 year old Rev Frederick Torrens, who also baptised some of the children of James Gray and Hannah Elizabeth Henry.  She had taken two years off her age by the 1911 census!

U/1883/92/1008/9/36    Mary    Gray    28th October 1883    Female    Brewster    Coleraine(pre-1973 Q4)

Civil Birth Record
Name:    Mary Allen Boyd Gray    Date of Birth:    28-Oct-1883
         Registration Date:    1-Jan-0
Address:    Englishtown    Parish/District:    AGHADOWEY
Gender:    Female    County    Co. Derry
Denomination:    Registrar District
Father:    William Gray    Mother:    Ann Brewster
Occupation:    Labourer    
Sponsor 1 /
Informant 1:    William Gray    Sponsor 2 /
Informant 2:    
Notes:

Buried in the New Cemetery, Presbyterian Church, Ballymoney along with her husband, Sam McShane.   

Date of Birth = Macosquin Presbyterian Church Births Register.  1901 census aged 14 confirms.  As does General Registry Office Births Index (I did NOT look at the actual record), where she is given as AnnIE Maggie.

Civil Birth Record
Name:    Annie Maggie Gray    Date of Birth:    06-Jul-1886
         Registration Date:    1-Jan-0
Address:    English Town    Parish/District:    AGHADOWEY
Gender:    Female    County    Co. Derry
Denomination:    Registrar District
Father:    William Gray    Mother:    Annie Bristo
Occupation:    Labourer    
Sponsor 1 /
Informant 1:    William Gray    Sponsor 2 /
Informant 2:    
Notes:

Date of Death = Dorothy Ferrone.

Anna Galbraith
SSN:    095-09-8826
Last Residence:    12508  Beacon, Dutchess, New York,
United States of America
Born:    6 Jul 1886
Last Benefit:    12508  Beacon, Dutchess, New York,
United States of America
Died:    Jul 1980

Birth record, taken from Letterkenny Local Registry Office, shows that Willaim John was born on 3rd January 1888 at Macosquin to William Gray of Englishtown, Labourer, and his wife, Anne Gray formerly Brewster and that his father registered the birth on 17th January 1888.

Civil Birth Record
Name:    William John Gray    Date of Birth:    03-Jan-1888
         Registration Date:    1-Jan-0
Address:    Englishtown    Parish/District:    AGHADOWEY
Gender:    Male    County    Co. Derry
Denomination:    Registrar District
Father:    William Gray    Mother:    Anne Brewster
Occupation:    Labourer    
Sponsor 1 /
Informant 1:    William Gray    Sponsor 2 /
Informant 2:    
Notes:

This is the death notice taken from a clipping in the family album: "Mr William J Gray Garvagh.  One of Garvagh's most esteemed residents, Mr William John Gray, passed away on Thursday last week at his residence, The Gables.  He had been confined to bed for the last three months.  A native of the Macosquin district, Mr Gray moved to Garvagh over 50 years ago.  He was a well known building contractor and he retired from business some seven years ago.  Mr. Gray gained the esteem of everyone by his great integrity and kindly unassuming manner.  He was highly gifted and was a craftsman of unusual skill and perception.  His passing is much regretted by many friends.  Mr. Gray, who was a faithful member of Main Street Gravagh Presbyterian Church, Garvagh, is survived by his wife (formerly Miss Jean McClements); his son, Samuel, who resides at Ballykelly and four daughters - Miss Sadie Gray SRN, Mrs. McWilliams, Larne; Mrs. Atkinson, Tonbridge, Kent; and Mrs Pink, Surrey.  The funeral, which was largely attended, took place on Saturday afternoon to First Garvagh Presbyterian Church burying ground, Rev D. H. Allen B.A, officiated in the home and at the graveside."  (NB - there is a discrepancy here: if he was a faithful member of Main Street Presbyterian Church, which is 2nd Garvagh, why is he buried in 1st Garvagh on the Kilrea Road?)

Registration number    Forename of deceased    Surname of deceased    Date of death    Age at death    Date of birth    Sex of deceased    Registration district    
D/1961/95/1008/14/257    William    Gray    6th April 1961    73        Male    Coleraine(pre-1973 Q4)

Date of Birth = Macosquin Presbyterian Church Births Register. 1901 census gives her as 12 = Date of Birth of 1889 again.  By 1911 she is 21 according to the census.

name:     Sarah Matilda Galloway Gray
registration district:     Coleraine
event type:     BIRTHS
registration quarter and year:     Jul - Sep 1889
estimated birth year:    
age (at death):    
mother's maiden name:    
film number:     101062
volume number:     1
page number:     409
digital folder number:     4193976
image number:     00535

Registration number    Forename of child    Surname of child    Date of birth    Sex of child    Mother's maiden name    Registration district    
U/1889/92/1008/11/54    Sarah    Gray    7th July 1889    Female    Brewster    Coleraine(pre-1973 Q4)

Civil Birth Record
Name:    Sarah M G Gray    Date of Birth:    07-Jul-1889
         Registration Date:    1-Jan-0
Address:    Englishtown    Parish/District:    AGHADOWEY
Gender:    Female    County    Co. Derry
Denomination:    Registrar District
Father:    William Gray    Mother:    Ann Brewster
Occupation:    Labourer    
Sponsor 1 /
Informant 1:    William Gray    Sponsor 2 /
Informant 2:    
Notes:
CHILD'S FULL NAME: SARAH MATILDA GALLOWAY

Gravestone in Macosquin Presbyterian Church says, "their twin son died in infancy".  General Registry Office Births Index shows no twin for any of Mary in 1883, Anna Maggie in 1886, Derry Family History Centre Index shows no twin for William in 1888 or Sarah in 1889.  I think I have him!!  Derry FHC Deaths Index shows a Robert Gray, Coleraine, aged dash, 4th Quarter, 1888.  This makes him a twin of my grandfather, William Gray.  Sent to Dublin for death entry - problem with Index number which is partly illegible (1.3?5).  Unfortunately, this turned out to be a blacksmith from Garvagh - so - back to square one!

I compared the births of all four siblings with other Grays Births in Coleraine Registry District to see if another child was listed on the same page and found none:
"Mary" is 1.460 in the 1st Q of 1883 - a Robert Wilson Gray was on page 1.441 of this quarter.
"Anna Maggie" is 1.149 in 3rd Q of 1886 - a David Gray is on page 1.429 of this quarter.
"William John" is 1.445 in 1st Q of 1888 - no other Gray births
"Sarah Matilda Galloway" is 1.409 in 3rd Q of 1889 - no other Grays
 

Gravestone in Macosquin Presbyterian Church says, "their twin son died in infancy".

I wonder could this be him:
D/1886/94/1008/13/341    David    Gray    29th June 1886    0        Male    Coleraine(pre-1973 Q4)    Enhanced
Full
Order certificate
D/1886/92/1008/7/47    James    Gray    4th September 1886    0        Male    Coleraine(pre-1973 Q4)

Nope:
Registration details
Registration number
D/1886/92/1008/7/47
Registration district
Coleraine(pre-1973 Q4)
Registration sub-district
Aghadowey
Deceased details
Deceased name(s)
James Gray
Sex of deceased
Male
Marital status of deceased
Single
Date of death
4th September 1886
Age at death
0
District of death
Coleraine(pre-1973 Q4)
Elizabeth Gray, mother of deceased, was PAD, he was from Curragh, Macosquin, aged 11 weeks old and died of meningitis and was the son of a labourer.  I wonder is this him because 11 weeks before 4 Sep is not far away from 6th July, when Anne Maggie was born.  Also, Wliiam's father was called James so one would expect his first son to be called James.  But, Elizabeth would need to be Annie.  I can find no James Gray born to either an Ann or an Eliza in 1886 in RootsIreland in 1886.