I though the father was pityful but he reap that he sow, Mielle was just a joke at the end "I was jalous about Aria, try to humiliate her, frame her about a crime and finnaly kill her but now that I lost all my money and peerage I find her quite cool, I'm sure she will help me, we are sister after all" XD
I have some pity for the bro, he was a real human trash but repent and really try to restard a new life.
I think the way Mielle broke down that way was splendid mental manipulation by Aria. the kind of Good Cop-Bad Cop -kind of manipulation. Aria emphasized the fact that she never did directly took revenge on her despite her being so hard on Aria. thats why Mielle saw Aria in a kind light, that she was this savior who forgave all she had done wrong. and she became dependent on her the way she was dependent on her maid
Mielle was basically dependent on her maid and the Crown Princess anyways and at the moment Aria got her Maid killed, Aria has already won.
because at the end of the day, Mielle is one of your basic spoiled noble daughter who doesnt know basic anything beyond trying to be pretty and sucking up to the Crown Princess.