In the introduction to Pandemonium: Ethnicity in International Politics, the late Sen. Daniel Patrick Moynihan (D-N.Y.) quoted Walker Connor defining a nation as “a group of people who believe they are ancestrally related. It is the largest grouping that shares that belief.”
First, note the word “believe.” It is possible for people who aren’t technically ancestrally related to believe that they are. Trump endorser Rick Santorum, the descendant of Italian immigrants and defender of immigration restrictions past and present, believes he is as American as anyone who can trace their ancestry back to the Mayflower. Nation-states can break apart if the people, regardless of actual lineage, do not share that belief.
Second, family is a constructive way of distinguishing healthy and unhealthy nationalism. You love your family because it is yours. Your family members’ accomplishments and strengths may enhance your love for them, but they are “exceptional” to you in the first place because those familial bonds exist.
Your love for your family does not require you to hate other families, to view their members as inferior, less than human, or undeserving of rights. It certainly does not require you to fight with other families or take over their homes.