Responses
Because those are the laws of the isekai world. Yvonne is the heroine, so she gets immunity, plot armor, etc. whatever you wanna call it. Penny instead is stuck as the villainess, so things hardly ever will going to go her way.
Also, Penny didn't "stay with them their entire life", it's only been six years. She was already twelve (I think?) when she was adopted by the duke. Please correct me if I'm wrong because I don't remember the age difference among the siblings.
Why all the characters in this one lack emotional intelligence? Excluding Penelope of course, but even tho Yvone appears all the peoples score point will decrease like she have anything to do with the other girl and even if she was bullied or even poisoned people around her specially her brothers will have to most bullshit reaction like bro even you are a comic character how come they lack humanity or a living being you stayed for your entire life. Wtf seriously it makes me so mad i guess the reason i am continuing this one coz i want to see the downfall of those emotionless creatures..