John Gill Commentary 1 Chronicles 26:21

"The sons of Ladan, the sons of the Gershonites belonging to Ladan, the heads of the fathers` [houses] belonging to Ladan the Gershonite: Jehieli." — 1 Chronicles 26:21 (ASV)

As concerning the sons of Laadan
The same with Libni, see (1 Chronicles 23:7)

the sons of the Gershonite Laadan ;
so called, to distinguish him from another Laadan, as Kimchi thinks:

chief fathers, even of Laadan the Gershonite ;
that sprung from him: were Jehieli; and his sons next mentioned.