وَوَلَدْنَا عَمْرَو بْنَ أُمِّ أُنَاسٍ مِنْ قَرِيبٍ لَمَّا أَتَانَا الْحِبَاءُ
Meaning: We also acquired close kinship with ʿAmr son of Umm Unās through marriage, when the marriage payment came to us.
Waladnā ʿAmran here serves a boast about lineage and marriage ties, not merely a report of one childbirth. The commentary connects Umm Unās with a marital relationship and al-ḥibāʾ with the payment given in that context.
Lammā atānā is a temporal clause meaning “when it came to us.” The poet is laying a foundation for the argument that kinship should produce sincere political counsel, made explicit next.