Laura 1855 Abel and Virginia 1857 Abel are in the 1880 census with Richard and Susan but they are not in the 1860 or 1870 census. They are probably nieces.

Name: Richard L Abel [Richard T Abel] 
Age: 55
Birth Date: May 1845
Birthplace: Virginia
Home in 1900: Rock Hill, Stafford, Virginia

Relation to Head of House: Head
Marital status: Widowed
Father's Birthplace: Virginia
Mother's Birthplace: Virginia
Occupation: Farmer
Farm or House: F
Neighbors:
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Household Members:
Name Age
Richard L Abel 55
Laura Pearson 50
Mary V Pearson 46
Jennie Carter 40

The following shows that Richard’s wife, Susan A, was Susan A Pearson:

Name: Susan M Abel
Age in 1870: 35
Birth Year: abt 1835
Birthplace: Virginia
Dwelling Number: 27
Home in 1870: Dumfries, Prince William, Virginia
Inferred Spouse:
Richard T Abel
Household Members:
Name Age
Richard T Abel 34
Susan M Abel 35
Laura Pierson 33
Jennie Pierson 31 (Mary Virginia “Jennie”)
Thomas E Carter 23

Name: Mary V Pearson
Age: 46
Birth Date: Jan 1854
Birthplace: Virginia
Home in 1900: Rock Hill, Stafford, Virginia
Sheet Number: 3
Number of Dwelling in Order of Visitation: 53
Family Number: 53
Race: White
Gender: Female
Relation to Head of House: Son in Law
Marital status: Single
Father's Birthplace: Virginia
Mother's Birthplace: Virginia
Household Members:
Name
Age
Richard L Abel 55
Laura Pearson 50 (Laura above)
Mary V Pearson 46
Jennie Carter 40 (Husband Thomas E Carter)