He and his wife were first cousins through their mothers who were sisters.

His birth index:

First name(s)         HENRY G
Last name             HARDING
Birth year            1866
Birth quarter         1
Mother's maiden name  Read
District              Stratford on Avon
County                Warwickshire
Country               England
Volume                6D
Page                  567
Record set            England & Wales Births 1837-2006
_______________

His baptism transcription from FamilySearch:

Name:                      Henry George Harding
Gender:                    Male
Christening Date:          25 Jan 1866
Christening Place:         HOLY TRINITY,STRATFORD ON AVON,WARWICK,ENGLAND
Father's Name:             William Feilding Harding
Father's Residence Place:  Shottery
Mother's Name:             Emily  [sic]

Once more William gave his mother's name as the name of the mother of his child.
___________________

In 1891 he and Edith were at Baraset House, Alveston, Stratford on Avon, Warwickshire:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place
Henry Geo  Harding   Head          Married  Male    25  1866  Living On Own Means  Shottery, Warwickshire
Edith G    Harding   Wife          Married  Female  23  1868  -                    London, Middlesex
Katherine  Steward   Wifes Sister  Single   Female  20  1871  -                    London, Middlesex
Selina     Timms     Servant       Single   Female  28  1863  Cook                 Alveston, Warwickshire
Caroline   Mound     Servant       Single   Female  23  1868  Parlourmaid          Worcestershire
Alice      Hurdwell  Servant       Single   Female  27  1864  Housemaid            Sandhurst, Berkshire
Lily       Kirby     Servant       Single   Female  17  1874  Kitchenmaid          Richmond, Surrey

Ref:
Archive reference  RG12
Piece number       2476
Folio              14
Page               22
Combined:          RG12, piece 2476, folio 14, p. 12
___________________

In 1901 Henry was not at home, nor was William but the rest were at 19, Lower Belgrave Street, St George Hanover Square, London & Middlesex:

First name(s) Last name Relationship Marital status Sex Age Birth year Occupation Birth place
Edith Harding Head Married Female 33 1868 Living On Own Means Bayswater, Middlesex, England
Gwendolen Harding Daughter - Female 7 1894 - London, England
Basil H Harding Son - Male 3 1898 - Belgravia, London, England
Lionel P Harding Son - Male 2 1899 - Belgravia, London, England
Elizabeth H Purkis Servant Widow Female 47 1854 Cook Domestic Hampshire, England
Eliza Barrow Servant Widow Female 47 1854 Nurse Domestic Ringwood, Hampshire, England
Sophia Hughes Servant Single Female 17 1884 House & Parlour Maid Ecclesfield, Yorkshire

Ref:
Archive referenc  RG13
Piece number      85
Folio             42
Page              27
Combined:         RG13, piece 85, folio 42, p. 27

___________________

In 1911 they were at Manor Croft Station Road Thames Ditton, Thames Ditton, Surrey.  He wrote that he had had four children who were all slive:

First name(s)  Last name  Relationship  Marital status  Sex  Age  Birth year  Occupation  Birth place
Henry George  Harding  Head      Married  Male    45  1866  Nil                            Strotting Stratford on Warwickshire Devon
Edith G       Harding  Wife      Married  Female  43  1868  -                              London Bayswater
William O F   Harding  Son       Single   Male    18  1893  Clerk In Oil Company's Office  Herts Wheathampstead
Gwendoline    Harding  Daughter  Single   Female  17  1894  -                              London S Kensington
Emily         Major    -         Single   Female  28  1883  Domestic Servant               Middlesex Hanworth

Someone had added that he was a “Retired colonel E…..” and his birth place was “Shottery, Stratford on Avon, Warwickshire”.

Ref:
Census reference  RG14PN3552 RG78PN133 RD40 SD4 ED4 SN234
RG78 code number  133
Piece number      3552
_________________

The birth os their children:

Name:                                 Mother's Maiden Surname:
HARDING, WILLIAM  OLIVER FEILDING     STEWARD  
GRO Reference: 1892  J Quarter in SAINT ALBANS  Volume 03A  Page 571
HARDING, GWENDOLINE                   STEWARD  
GRO Reference: 1894  M Quarter in KENSINGTON  Volume 01A  Page 161
HARDING, -                            STEWARD  
GRO Reference: 1897  S Quarter in ST GEORGE HANOVER SQUARE  Volume 01A  Page 462
HARDING, LIONEL  HENRY POWYS          STEWARD  
GRO Reference: 1898  S Quarter in ST GEORGE HANOVER SQUARE  Volume 01A  Page 463

Was the third child one George Trevor Hamilton?
_________________

Their marriage index:

Surname First name(s) District Vol Page
Marriages Jun 1890   (>99%)
Harding Henry George Kensington 1a 290
Steward Edith Georgina Kensington 1a 290

They were first cousins, their mothers being sisters.
________________