Pia

Pia worked alongside her Mother in leading the Brethren.

Personality
Pia is power hungry, hates to be talked down to and is quite arrogant, calling Edgardo and Harlan "little nothings" and claims they are privileged to lay eyes on her, as "scum like you aren't fit to lick my feet!"

She has a clear sadistic streak, enjoying electrocuting the pair, wishing to hear them scream in pain for her.

She did most of this in an attempt to impress her mother, which appeared to be unnecessary. This implies she had a healthy relationship with her mother.

Killed Victims

 * Possibly other captured Vampires

Death
Failing to notice Edgardo and Harlan exiting the Werewolf corpses they were hiding in, Eduardo comes up behind her and rips off her head. He immediately attempts to desecrate her carcass by "shitting down her throat" as he promised earlier, but is interrupted by Mother.
 * Herself(Indirectly)
 * Edgardo

Mother
Pia seemed to want to make her mother proud and even impress her, which seems to have been unnecessary as her mother clearly cared for her. She even goes as far as comforting and reassuring Pia when she became distressed by losing the captured Vamps, even patting her head. When Pia is killed, her Mother becomes enraged and immediately attempts to avenge her death by killing the Vamps.

Desmond
Desmond acknowledged Pia as "Mistress Pia" after acknowledging the Master, implying he respects her.

Uncle
He didn't seem to angry when told of her death, but he seems like the kinda guy to think of her as a brat.

Edgardo
This may surprise you, but they obviously had a very hostile relationship.

Trivia

 * She is presumably a Werewolf, though she is never seen turning into one.