Conversations is for RP, Messenger is for OoC. Things will always be post P5 events.
Caroline and Justine, or Lavenza, are characters from Persona 5. They are the younger sisters of Margaret, Elizabeth and Theodore and attendant(s) of the protagonist of Persona 5.
Caroline has a very classical tsundere (someone who acts mean-spirited and aloof to disguise any affectionate feelings) attitude towards the protagonist. Additionally, she doesn't seem to hold the protagonist in very high regard, as she refers to him as "inmate," and kicks him into the Velvet Room whenever he goes to enter.
Justine, in contrast, appears to be calm and soft-spoken, but still treats the protagonist as her prisoner, often addressing him in a condescending tone. Unlike her sister, she will calmly escort the player to their cell.
Despite the twins' usually haughty behavior, in Persona Q2, the relationships with their older siblings are further expanded. They respect their older siblings and don't seem to treat Theodore in a particularly disrespectful manner, unlike Margaret and Elizabeth. Similar to Theodore, they also fear angering Margaret, as seen during a fusion accident.
Lavenza speaks relatively more maturely and politely than the twins, while also retaining certain traits from both. She also refers to the protagonist as trickster, instead of inmate. Like Justine, she maintains a soft-spoken tone, though without the condescension. Like Caroline, she is shown to lose patience easily, as shown when Ryuji expresses confusion towards her explanation, or when she fails to craft a tool and almost ends up casting Megidolaon on the work table out of frustration. When frustrated, Lavenza may change her vocal tone to match Caroline's. Lavenza may doze off easily when sitting on soft surfaces. She also has a mischievous side, as shown in the Thieves Den when she gives Ann and Makoto permission to sit at Igor's desk while he is away, despite considering doing so a "forbidden ritual."