Why does Pucci want to separate the weather?

As for Pucci's three brothers and sisters, I read in the comments that the weather and Pella are close relatives, and even if they get married in the future, they will be deformed, so Pucci won't let them get hurt.

My understanding is that Pucci was replaced, and Pera was born to Pucci's foster mother. So Pucci is related to the weather, and neither of them is related to Pera. So why did Pucci break up two people, so as not to hurt his sister? Where did you hurt your sister?