Sydney and his brother Walter Knibbs married the sisters Alice and Eliza Wastell.

Sidney's father, Henry Theodore Knibbs isn't strictly a member of the Knibbs family. His parents were John and Ann BURT so his real name is Henry Theodore BURT. Henry's mother was widowed and then married Francis Knibbs (1793-1856).
Henry married as Henry Theodore BURT but at a later date, he assumed the surname KNIBBS.
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Sidney and his family can be seen in 1891living with his wife Alice and two daughters Alice and Grace at the home of his father, Henry at 9 Little Coram Street, St George, London, Middlesex. The household seems a little mixed and a struggle to understand who is who.
Henry Knibbs Head Widr 63 Beerseller Somersetshire
Sydney Knibbs Son M 26 Manager St George's East
Alice Knibbs Wife M 26 Middlesex
Alice Knibbs Dau 2 Bloomsbury, London
Grace Knibbs Dau 8 Bloomsbury, London
Lizzie Knibbs Wife M 56 Middlesex
Walter Knibbs Son 9 Middlesex
Alice M Dau 6 Bloomsbury, London
Eleanor Knibbs Dau 5 Bloomsbury, London
Frank G Knibbs Son 2 Bloomsbury, London
Herbert Knibbs Son 20 Homerton
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Sidney can be seen in 1901 living at 33 Commercial Road, Whitechapel, London, Middlesex, England, but with no other Knibbs family members, although the census identifies that he is married.
Sydney Knibbs 37 London London Whitechapel Beer Retailer

His wife and children are listed in the census but living at 7 Anam Street, Whitechapel, London, Middlesex. My theory is that Sydney was working a the time of the census whereas his wife and children were at home. Also living with his Sydney's wife at the time was Sydney's brother Alfred:
Alfred Knibbs 40 Boarder St George in the East London
Alice Knibbs 36 Wife (husband absent) Bethnal Green London
Alice Knibbs 12 Dau Scholar Bloomsbury London
Grace Knibbs 10 Dau Bloomsbury London
Ada Knibbs 8 Dau Bloomsbury London
Sydney E 7 Son Bloomsbury London
Florence Knibbs 2 Dau Plastow London
Victoria G Knibbs 2mnths Dau Whitechapel London
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We can see Sidney and his family in 1911, living at Stepney, London, Middlesex:
Knibbs Sidney M 1864 47
Knibbs Alice F 1865 46
Knibbs Alice F 1889 22
Knibbs Grace F 1891 20
Knibbs Ada F 1893 18
Knibbs Sidney Edwin M 1894 17
Knibbs Florence F 1899 12