You are kings but Ugrasena is the ruler or king of you (ksiti isa isa). Why? Because he is master (prabhu), whose order Indra and others carry out, offering him tribute in the form of the sudharma hall and the parijata tree. Yayati forbade the Yadus from being kings, but he did not forbid them from being rulers of kings. You should listen carefully to his order, otherwise he will punish you.

Since Ugrasena is the lord of the earth, you should obey his order. He is also the giver of orders to great kings (prabhuḥ). He was not called a king because Yayati had forbidden the Yadus to be kings (since Yadu refused to give Yayati his youth). That you should obey him is also reasonable since you are careful people (avyagra-dhiyaḥ). Or he says this to put them at ease. Be peaceful (avyagra-dhihaḥ). Do not be fearful, worrying about what will happen.

His order should be followed because he is the lord of kings (kṣiteśeṣaḥ) since he is the lord of us Yadus (prabhuḥ). Or he is the lord of all people (prabhuḥ). You should carefully hear his order. Balarāma speaks in this way to destroy their pride as kings and make them angry and to show his own bravery. And out of compassion he wanted to make the foolish persons intelligent. That is revealed later.