Genealogy traces the biological parents of an individual. This means one male and one female.
If you want to trace other relationships, such as adoptive parents, foster parents, god parents, guardianships, co-habitating individuals, or even a marriage that is not one male and one female, you can indicate this in the Biography section.
Note that the biological mother and father of a profile do not have to be married to each other. There is even a check box to not show them as married in each other's profiles.