Bo Qiliu and Bo Yi were not unaware of Bo Yan's abilities.
If Bo Yan's father hadn't died, the old man planned to groom him to be the heir. Bo Yan was smart from a young age, the type where Bo Yi had to work desperately hard while Bo Yan played games every day and still easily outperformed him. But with Bo Yan's father's death, Bo Qiliu saw his chance. Especially since later on, the old man was either too busy with work to raise Bo Yan, or feared that he might seize power when grown, so he clearly still cared for Bo Yan but didn't prioritize him as much. In contrast, he valued Bo Yi more.
