Short answer
Biradari preference is a social consideration and should not automatically be treated as an absolute Islamic rule.
Islamic Guidance
What Islam teaches
Islam emphasizes justice, good character and piety rather than pride in lineage or social status. Family advice is important, but cultural customs should not be presented as divine requirements without evidence.
Practical Guidance
What you can consider
Parents and children should discuss the reasons objectively. If disagreement continues, involve a knowledgeable and trusted person who can distinguish Islamic guidance from local custom.
Sources
Qur'an 49:13.