Hi,

Sometimes you have to look for name changes between census periods.
I'd take a close look at this family in 1870:

Name: Sarah Darley - head of household
Estimated birth year: abt 1835
Age in 1870: 35
Birthplace: South Carolina
Home in 1870: Schley, Georgia

Race: Black
Gender: Female
Post Office: Ellaville

Sidney Darley
Estimated birth year: abt 1857
Age in 1870: 13
Birthplace: Georgia

Name: Henry Darley
Estimated birth year: abt 1862
Age in 1870: 8
Birthplace: Georgia
Home in 1870: Schley, Georgia

Other listed children - Rubin and Eliza.

She is listed as born SC.

Your Sidney in 1880 has mother listed as NC in index but it could be SC on actual record.

Name: Sir Oliver
[Sid Oliver]
Home in 1880: District 961, Schley, Georgia
Age: 25
Estimated birth year: abt 1855
Birthplace: Georgia
Relation to head-of-household: Self (Head)
Spouse's name: Melia
Father's birthplace: GA
Mother's birthplace: NC
Neighbors: View others on page
Occupation: Farm Work
Marital Status: Married
Race: Black
Gender: Male

Household Members: Name Age
Sir Oliver 25
Melia Oliver 23
Shate Oliver 2

For Amelia (Melia) there are 2 possibles in 1870:

Name: Meley Dinkins
Estimated birth year: abt 1857
Age in 1870: 13
Birthplace: Georgia
Home in 1870: Schley, Georgia
Family and neighbors: View Results
Race: Black
Gender: Female
Value of real estate: View image
Post Office: Ellaville

Name: Melley Snipes
Estimated birth year: abt 1858
Age in 1870: 12
Birthplace: Georgia
Home in 1870: Schley, Georgia
Family and neighbors: View Results
Race: Black
Gender: Female
Value of real estate: View image
Post Office: Ellaville