Barzum mostly has a demure and worried personality, and is noted to speak in a monotonous and incredibly quiet voice. She is first seen bearing a worried and hesitant countenance, almost appearing to be sad. The player mentions that her words are quite hard to pick out, since her voice is so soft. However, Barzum also appears to switch personalities with Baizli, adopting his loud and brash manner of speaking. When truly irate, Barzum can be seen snarling at the player, furious with the player for wanting to leave so soon. 

On the other hand, Baizli starts off with a shrill and dramatic persona; hollering his words as though he'd never heard of the term 'indoor voice'. The moment the player gets a clear look at his featuers, they note that he has a manic gleam in his eye that matches the wicked grin on his face. Yet, he swaps this trait with his sister, becoming sad and close to tears when the player expresses their intent to leave the house as quickly as possible. 

The twins have a morbid fascination with blood colour and other gory details--right after learining that the player's an alien, the twins are curious as to whether the player's intestines would writhe around if they cut the player's stomach open. When the player swaps stories with the twins, the player mentions that it's hard for them to not cringe upon hearing one of Barzum and Baizli's more gruesome stories. 

However, the twins aren't noted to be as sadistic as they appear to be; when the player tries to make a deal with the twins (letting the player live so that the twins would have a playmate), Barzum and Baizli are shocked that the player assumes that the purplebloods would kill them off. The player deduces that since no one told the twins that not every troll or being heals as quickly as highbloods, Barzum and Baizli automatically assumed that anyone would bounce back from their injuries as quickly as they do. Once that little misunderstanding is cleared up, the twins are more than eager to showcase their skills to the player. 

I'd imagine both of them sounding like the twins from The Shining.