This morning I've been lucky!

It's not easy to track this family because the surname keeps changing from census to census.
My initial idea was that William Spear's wife (Mary Ann) had died, and I found a death entry on FreeBMD of a Mary Ann SPEAR d. MAR qtr. 1860 at Hartismere (Suffolk), but it seems I was wrong, since I've found the whole family in the 1861 Census but with the surname
SPIRE
William Spire Head M 50 Rickinghall, Suffolk
Mary Ann Spire Wife F 45 Rickinghall, Suffolk
Eliza Spire Daughter F 24 Mendlesham, Suffolk
Hannah Spire Daughter F 17 Mendlesham, Suffolk
Henry Spire Son M 14 Mendlesham, Suffolk
Emma Spire Daughter F 9 Mendlesham, Suffolk
Deborah Spire Daughter F 4 Mendlesham, Suffolk
Mary Ann Spire Granddaughter F 4 Mendlesham, Suffolk
Nathan Chiles Visitor M 19 Mendlesham, Suffolk
(Source: FamilySearch)
(Underlined are the family members I am interested in. Now I would like to find birth, baptisms, marriage and deaths places and dates about them).
Any help, would be greatly appreciated!
PS: How would I know which one is the correct surname: Spear, Spears, Spere, Spier, Spiers, Spire?
And why does it change so much (a transcript error, or was it such an uncommon surname in the region)?