Ibn Ezra on Numbers 36:12

ממשפחות. לאות כי בני דודיהן לא היו כולם אחים: THEY WERE MARRIED INTO THE FAMILIES. This¹¹The word families. is a sign that their cousins¹²The cousins who married the daughters of Zelophehad. were not all brothers.¹³If they were, then Scripture would have read, they were married into the “family” rather than they married into the “families.”