דברי הימים א, פרק ט״ו, פסוק ה׳

The organization of these ancient families played a crucial role in their assembly. The family tree of Kohath was uniquely structured, dividing into multiple distinct ancestral houses. His sons Amram and Izhar were grouped together to form a single family unit, while another son, Hebron, stood entirely on his own as a separate family. Meanwhile, the line of Uzziel branched out into two distinct groups: one for Uzziel himself and another for his son Elizaphan. This complex branching stood in sharp contrast to the groups of Gershon and Merari, who each remained as one single, unified family [מלבי״ם].

From within these various Kohathite families, a specific group was gathered. They were led by Uriel, the appointed chief in charge of the assembly. He was joined by his brethren, referring to his close associates and the members of his specific ancestral house [מצודת דוד, ביאור שטיינזלץ]. Together, this entire company of men numbered exactly one hundred and twenty.