What is the ruling on differential treatment of children by parents, what is the ruling on siblings attempting to spoil the relationship between a son and his parents, and what can the son do regarding these circumstances?

The doer of good is rewarded for his dutifulness to his parents, even if they deny him. He must be patient and seek the reason for any misbehavior on their part. If the siblings cause discord between the son and his parents, this is a grave evil that necessitates advice and reminders of Allah.