He was either my grandfather or was married to my grandfather's sister

Name - "official" name and what they were known as
Henry William Wicks, often known as H W Wicks – (Googling brings up results for both)

Date and place of birth
17th July 1893 – Poplar, London

Names of parents –
Henry Wicks & Annie E Wicks (nee Payne)

Details of each of his or her marriages - if any - and any divorces
11th Dec 1915 to Mary Suzette Syms at the Unity Church and Hall, Wood Green

27th December 1918 to Caroline Ruth Dowsett at the Presbyterian Church, Brighton

(On 8th August 1918 Caroline Ruth Dowsett married Clarence Thomas Platt at Preston Parish Church, Brighton – there is a possibility that Clarence Thomas Platt was really Henry William Wicks, and that this was some sort of insurance scam – but I now think that this is unlikely)

Occupation(s) - if any
Insurance Manager, inveterate litigator, broadcaster of pro-nazi propaganda from Berlin to England in WW2.

Military service - if any - none found

Addresses where they lived - and please list which censuses you have or haven't found him/her on, if applicable.
1901 Census – aged 7 in Walthamstow
1911 Census – Clerk for Insurance Company in Kingston
Numerous addresses including London, Liverpool, Brighton, Bournemouth, Redhill, Germany, France and Malta – also spells in HMP Wormwood Scrubs and HMP Parkhurst

Date, place and cause of death
2nd April 1979 Horley “on the way to Redhill Hospital” – coronary Thrombosis, Arteriosclerosis and Diabetes Mellitus

Date and place of burial / cremation. – not looked for
Details of will / administration of their estate - if applicable – not known
Memorial inscription - if any – not known