There, they saw them singing. After that, Carole asked them if the rumors about them were true and they denied them, laughing. They then explained they were Nonbinary. Due to the Mars radiation, they display more female characteristics than when they were younger, as they were born male.
Desmond then invited the girls to add their signatures to the collection of people they invited to their home. Desmond mentioned that there was only one person they ever loved, but their beloved died young. Since then, they found themselves unable to sing and decided to shut themselves from the world to spend their time with plants and AI. But in time, friends who heard their songs started visiting and they found the strength to continue singing.
When an AI tells Desmond it's time for their medication, they refused to take the medicine, insisting it was fine. They then sang another song, but ended up becoming unconscious. The AI then explained that Desmond wanted for them to listen to their last song and didn't take the medicine as its side effects make singing difficult.
They appear in a short scene where their AI asks them to wake up. They then awaken from this slumber to join Carole and Tuesday to sing the final song in episode 24.