Hi Bob,
Comparing 1851 to this in 1861 ? I'd be thinking Henry Morgan/Margan is not her brother...
1851: High Street, Chesterton
Head: Sarah Moore married 27, Inkeeper's wife, b Chesterton
Son: Henry Margan Moore 5, b Clare, Suffolk
Dau: Emily Margan Moore, 3, b Chesterton
Visitor: Henry Margan, unmarried, 36, Contractor in navigation, b London
Definitely looks like "Margan" to me
1861: High St, Chesterton
Head, Sarah Moor 40, married, Charwoman,
Son: Harry Moor 15
Dau: Elizabeth 10
Son: Reuben 6
Son: Tom 4
Dau: Sally 16m
Boarder: Harry Morgan 42, Cabinet Maker
All enumerated born Chesterton
MARRIAGE: 1872
Henry Morgan Moore, bachelor, engineer, of 70 Burleigh St, father Henry, coprolite merchant
Married 12 Jun 1872, Cambridge, St Andrew the Less
Mary Ann Crane , spinster, of 70 Burleigh St, father Thomas White, Shoemaker.
Interesting occupation on the father on the marriage - one wonders......

Do you have a birth registration of either of the 2 children on the 1851?
Cheers,
AMBLY