The Riverlands is the name of Malka's pride, and these are his and Nala's cubs.
Sambi: Was born after Nala, Tama and Kula fled from the Pridelands and found Malka's pride where Tojo, Mheetu and Chumvi were already living. Nala became the queen, and after she caught Malka attacking little Mheetu, she left him, later finding Simba.
The others are what could have been if Malka didn't attack Mheetu, and Nala didn't leave the pride.