The three Velvet Room siblings are Persona Q: Shadow of the Labyrinth downloadable content, but not as playable characters. Atlus made navigator voice DLC so you can have Elizabeth, Margaret, or Theodore replace Rise in battle.
Each navigator voice character costs 600 yen. All three characters are available today in Japan. Atlus has one more round of Persona Q: Shadow of the Labyrinth downloadable content scheduled for July 2 and it looks like Marie from Persona 4: Golden is a part of it.