Flatt & Scruggs (possibly with other members of their band) published a number of songs under the pseudonyms “Louise Certain” and “Gladys Stacy”. These were in fact the maiden names of their wives, and Louise Scruggs has an artist entry in her own right under her married name. However, it’s generally agreed that the real Louise and Gladys did not in fact write the songs attributed to Certain and Stacey.
There’s a somewhat similar case with Ruby Rakes; there was an actual Ruby Rakes, Carter Stanley’s half-sister, whose name Carter used to publish under. The MB entry for Ruby Rakes lists birth & death dates for the real Ruby, which seems a little misleading. In this case, I think Ruby Rakes would be better handled as an alias for Carter Stanley.
For Certain and Stacey, I could enter them as aliases for Scruggs and Flatt respectively, although I’m not sure they exactly map. The BMI website seems to treat them as such, though - a search for either Louise Certain or Earl Scruggs returns the exact same list of songs.
Another option might be to enter “Louise Certain and Gladys Stacey” as a group. As far as I know, any works credited to them were published under both names. There is something of a precedent for this in the Nanker Phelge entry.