‘And Isaac answered and said to Esau, “Behold I have made him your lord, and I have given to him all his brothers for servants, and I have sustained him with corn and wine. And what then shall I do for you, my son?”
Isaac too finds himself helpless. Had he not intended such favour to his elder son that he gave him everything there would have been something left. But he had intended to leave nothing for Jacob. So there is nothing left.
It demonstrates what had been the singlemindedness of Isaac's purpose that he thinks this. He knows what he had intended. Jacob was to be left out of the reckoning.
“All his brothers for servants.” This would seem to confirm that there were other brothers. Alternately it may signify the whole tribe as ‘brothers' (consider Genesis 19:7 where it means fellow-citizens; 24:27 where it means kinsfolk; 31:46 where it means servant companions).