Short answer
They should first understand the family's actual concerns and try to address legitimate issues respectfully.
Islamic Guidance
What Islam teaches
Islam encourages maintaining family relationships while avoiding unjust discrimination.
Practical Guidance
What you can consider
Ask whether the objection concerns character, religion, safety or compatibility, or simply social status and biradari.
Sources
Qur'an 49:13; Qur'an 31:15.