Query 1,
I agree that Charles/James in 1851 are Nephews of Charles;
Charles Emmitt, 48, Ag Lab. born Pangbourne
Charles Emmitt, 24, Nephew, Unm, born Basildon
James Emmitt, 16, Nephew, born Pangbourne
Query 2,
Marriage was 1857 and Sarah is alive in 1861 Census.
Marriage;
Charles EMMETT to Sarah GREGORY
22 November 1857, Pangbourn, Berkshire
(Source Familysearch.Org)
No extra details as to Fathers names/occp
1861 Census
Bradfield, Berkshire
RG9/742/66/15
Charles Emmett, 31, Head, Mar, Gardener, born Baildon
SARAH Emmett, 32, Wife, Mar, born Pangbourne (1829)*******
George G Emmett, 7, Son, born Pangbourne
Charles W Emmett, 2, Son, born Bradfield
William Emmett, 5mths, Son, born Bradfield
Johathon Rummay, 36, Lodger, Unm, Ag Lab, born Sulham
FreeBMD has a Death Reg Dec 1863 for Sarah Emmett
GRO which now has ages if you log in (its free to register) has her age 37
EMMETT, SARAH, age 37
GRO Reference: 1863 D Quarter in COOKHAM Volume 02C Page 239
So birth c 1826
1871 Charles has his 2 youngest Sons with him.
1881 Charles is in Middlesex age 51, Gardener, Widower.
1891 he is in the Staines Union Workhouse in Stanwell, Middlesex.
EDIT;
George G Emmett c 1854 was born before the Marriage in 1857 so is likely reg as surname GREGORY