Family migration constitutes by far the largest form of entry into countries with established democracies. Yet, it remains widely neglected in the literature on public attitudes. One of the key challenges in researching this topic is its inherent complexity. Family migration involves not only the claims of outsiders seeking entry, but also those of insiders wishing to reunite with family members. To address both dimensions simultaneously, we designed a conjoint survey experiment using an innovative dyadic approach. Respondents were presented with hypothetical cases of aspiring family migrants, alongside their respective family members already residing in the destination country. Key attributes, such as financial resources and types of family relationships, were randomized for each pair. We conducted the survey with 5,000 respondents across France, Germany, Italy, Sweden, and the United Kingdom. Our results suggest that respondents pay close attention to the characteristics of the incoming family migrant, such as language skills, while also being concerned with the economic resources of the family member already residing in the destination country. These findings indicate that research on public attitudes cannot treat family reunification as just one among many immigration motives. Study designs must also systematically account for the status of the family member already living in the destination country.