The Lannister 'Nephrite' family needs an heir because Nostra, the current heir, is about to die due to old age.

All of the old man's children were present. On the outside, they appear sad because their father is dying, but on the inside, they only care about their position as heirs. The ungrateful children did everything that pleased their father. The position of heir causes family members to fight and harm each other

Animals are willing to kill their fellow humans just for a piece of meat. Regardless they are siblings.

Nephrite Pa Zarek sat leisurely on the chair, next to you. His face didn't bother pretending to cry or suffer like his little brothers and little sisters. No, he wasn't sure he would be the heir and he wasn't worried. If the heir is someone else. Nephrite Pa Zarek will be ready to kill them and shamelessly steal that position.

His sinewy fingers are massaging the back of your head, his other hand is gently patting your six-month pregnant belly. That's his pampering and comforting you.