Sibling rivalry can be a problem however siblings also can be very protective of each other and good company. Rivalry may be more of an issue if children sense that their caregivers or parents aren't very available or aren't treating the children as individuals with differences but also with value.
Disclaimer: Opinions are my own and the information is provided for educational purposes within the guidelines of fair use. While I am a Registered Dietitian this information is not intended to provide individual health guidance. Please see a health professional for individual health care purposes.