Are domestic servant's usually family, when the family is black too?

In 1870, Henry and Catherine Foster have a 58 year old woman, Harriet Mcgeehee, living with them. She is listed as a domestic servant. There are two other families of black Mcgeehee's living next door.

I'm wondering if Harriet could be Catherine's mother? And her neighbors, Catherine's brothers?

Would this be common?

Thanks,
Tanya