What did the ancients mean by "three fathers and six mothers"?

Stepfathers who live together, do not live together, and whose stepmother remarries are collectively called three fathers.

As for the six mothers, it should be the eight mothers, referring to the first mother, stepmother, foster mother, loving mother, married mother, mother-in-law and wet nurse, which are collectively called the eight mothers. There is a picture of three fathers and eight mothers in Yuan Li Bu San Mourning.