This may help solve the Cobb mystery:

1900 United States Federal Census Record
Name: Tatt Cobb
Home in 1900: Rome, Floyd, Georgia
Age: 17
Estimated birth year: abt 1883
Birthplace: Georgia
Race: Black
Relationship to head-of-house: Nephew
Occupation: View Image Image source: Year: 1900; Census Place: Rome, Floyd, Georgia; Roll: T623 196; Page: 5A; Enumeration District: 117.

AND

1900 United States Federal Census Record
Name: Mariah Cobb
Home in 1900: Rome, Floyd, Georgia
Age: 16
Estimated birth year: abt 1884
Birthplace: Georgia
Race: Black
Relationship to head-of-house: Niece
Occupation: View Image
Image source: Year: 1900; Census Place: Rome, Floyd, Georgia; Roll: T623 196; Page: 5A; Enumeration District: 117.

IN THE HOUSEHOLD OF:

1900 United States Federal Census Record
Name: Manerva Huggins
Home in 1900: Rome, Floyd, Georgia
Age: 36
Estimated birth year: abt 1864
Birthplace: Georgia
Race: Black
Relationship to head-of-house: Head
Occupation: View Image
RecordImage source: Year: 1900; Census Place: Rome, Floyd, Georgia; Roll: T623 196; Page: 5A; Enumeration District: 117.