Hey there, @njokueruchi! You are right - there could be hatred and rivalry among siblings in a family.
As always in social science it is extremely difficult to isolate the different factors that play a role in one's behavior and to observe them independently. That is why we cannot say that only poor parenting is causing siblings hatred. External events, extended family (e.g. grandparents, uncles, and aunts, etc), biological factors (e.g. inherited personal traits) could also influence the emergence of siblings' rivalry.

Even though, there is some research which shows that parental favoritism (meaning parent's preference of one of the siblings over the others) could influence siblings' relationship and cause rivalry and hatred.

Thanks for readining and commenting! I appreciate it!