Grace's life as a transmigrated side characters secret sister

Who the heck is Serenity?!

"This definitely isn't a hospital."...

Third Person Pov:

Grace stared up at the unfamiliar brunette in confusion. "Who are you... and who the heck is Serenity?!" 

"O ah boo ah" Wait what. Grace, realizing the noise had come from her, recoiled in horror. "What the... why did I sound like a baby just now?" She tried to speak once more, but was again met with incoherent babbling noises.  

"Oh my, look how talkative our little lady is Stephan." The brunette stated, happily scooping up the confused blonde. Turning to face the door, Grace could now see that there was another person in the room. "Indeed she is, Selena." a man (whom Grace assumed was Stephan)said. He had dark grey hair that was brushed neatly to the side and onyx colored eyes. He seemed to be older then the brunette and was wearing a butlers outfit, similar to the one Alfred from batman wore. 'Stephan' looked down at the blonde and smiled softly. Grace subconsciously returned it before turning her head to look around the room. 

To the left of the room there was a small white dresser tucked into the corner with a bookshelf installed over it. The wall to the right of the shelf had 4 pictures of a baby with blonde hair lined up in a neat row. A large window was set up behind the crib with white curtains that were tied in the middle with tan bows. Next to it was a mirror nailed to the wall with a small white armchair  underneath it. A small storage dresser with a lamp on it was left of the chair with a stand up lamp and a white nightstand desk to the right of it. 

"It's very... white." Grace thought. "But now isn't the time to be worrying about that, I need to figure out where I am."  "Oh" 'Selena' said, startled at the sudden movement of the child. She quickly set Grace down on a fluffy white rug next to the crib, thinking she wanted to be put down. Grace took the opportunity to grab onto the crib, using it to carefully pull herself up. "Gee that was tuff. Who would have known standing up as a baby was so hard?" Grace mused. Startled by a sudden gasp from behind her, Grace fell flat on her but. "Grr, seriously" The baby turned her head to send an angry glare to the brunette for making her fall. "Eek, I'm sorry m'lady." Selena apologized, rushing to help the fallen toddler up. "tsk.." the toddler clicked her tongue in annoyance, making both adults sweatdrop. Once she was back on her feet, Grace slowly made her way to the dresser next to her crib, Selena supporting her on her journey. Finally getting there she picked up a piece of paper that was on top of it. 'Serenity Catalina Alidora Margarita' were the words printed neatly on the page in gold ink. Grace looked up at the brunette in confusion. "Dis?" she said. "That's your name m'lady. Serenity Catalina Alidora Margarita, a beautiful name indeed." Selena said, smiling down at Grace/Serenity. A look of horror crossed the child's face. "The h*ll, why is it so long!! That's gonna be a pain to write out on tests" she thought. Just then there was a light knock at the door as a maid with dark blue hair and eyes popped her head into the room. "Sir Alpheus has requested we bring Lady Serenity and Lady Jeannette to his study" the maid said before leaving. "Whelp, looks like you'll be seeing your sister soon m'lady, though I don't understand why they even separated you in the first place, aren't twins normally supposed to stay together??" Selene said quizzically. 

 "Hold up, sister, twins, and did that maid just say sir Alpheus and Jeannette ?? As in 'Who made me a princess' Alpheus and Jeannette?" 

"What the h*ll is going on?!"