I believe it is this Joseph who appears in the 1901 census listed under his second name of William. His father was also named Joseph so it is quite likely that over the years his second name was used to avoid confusion.
Certainly in the following entry, "William" is of the right age, living in the same part of London as his father, mother and younger siblings, and has the same occupation as his father. His wife Alice was born in Poplar and to the best of my knowledge, this was the only Knibbs family living there at around this time.
William Knibbs 27 Warwick Birmham Laborer In Ship Yard
Alice Knibbs 20 London Poplar
Ivy Knibbs 4 months London Poplar
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We can see Joseph and his family in 1911 living at 29 East Ferry Road, Poplar, London, Middlesex:
Joseph William Knibbs Head Married M 36 General Labourer in Ship Birmingham Warwick
Alice Knibbs Wife Married (10 years) F 29 London Poplar
Ivy Sarah Knibbs Daughter F 10 School London Poplar
William Robert Knibbs Son M 8 School London Poplar
Alice May Knibbs Daughter F 6 School London Poplar
Violet Lilian Knibbs Daughter F 3 London Poplar
Eva Dorothy Knibbs Daughter F 2 London Poplar
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Joseph's granddaughter Linda tells me that Joseph and his wife Alice lived just two doors away from her house when she was a child. Joseph would go to her house very early in the morning when she was small and light the fire, so that when she got up the house was warm!
Linda's father used to shave her grandfather, with an open razor that her grandfather used to sharpen on a leather strop.
Her grandfather would tell her stories of when he sailed on the Clipper ships across the oceans!
Linda remembers him as a lovely, gentle man.

Unfortunately, there seems to be 3 Alice Smith's born in Poplar in 1880/81 so without knowing more of her family details, I'm not sure which family is hers.
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Alice with the two twins, Florence Elsie on the left and her brother Frank Leslie James aged at around 18-24 months