Yep. Crazy person that I am, I decided to give that particular set of twins some siblings. They actually had an older sister as well ... but she wasn't able to make it to Sleeping Beauty's party, so ...
But that's beside the point. You aren't here to learn about the elder sister who has very little effect on the book. You're going to have to wait until the book comes out to learn more about her.
I'm talking about Kim and Vern today.
Kim is the youngest of the Tune siblings at twelve. Her gift was a love for the science of plants. And she does love plants. She can talk about them all day if you let her. Like all the Tunes, she has a splendid singing voice, and can play almost any instrument. She does do better with a wooden instrument, though.
Vernon is the second youngest at fifteen, and his gift was a mechanical genius. Need something really crazy built - talk to him. Need your carriage fixed - talk to him. The only thing I know about his appearance is the fact that he's always covered with grease. Always.
However, the two of them did not grow up with Sam and Shira. When the siege occurred, they, and the oldest sister, went to a different castle, not Locksley. They all still sing well together, but they don't know Sam and Shira as well as they do Adelaide (who will be my next person! Heads up!), and Sam and Shira aren't as close to them as they are/were to Madeleine and Maximilian.
'Tis a sad state of affairs, but 'tis how it is.