Or HaChaim on Numbers 32:2/אור החיים על במדבר ל״ב:ב׳

1 ויאמרו אל משה ואל אלעזר ואל נשיאי העדה, and they said to Moses, to Eleazar, and to the princes of the congregation, etc. We need to know why they were not content to speak to Moses alone; if there was no need for them to address also Eleazar and the princes in the matter there was also no need for the Torah to report this. Perhaps the reason was simply that they had noted that when the general legislation about distributing the land of Canaan was made public in Numbers 34,17-18, Eleazar and Joshua as well as the princes were present. Also the daughters of Tzelofchod had made certain that Moses, Eleazar, and the princes were present when they presented their claim (27,2). In order for this distribution to be valid and not subject to complaints at a later date, it had to be confirmed by the king, i.e. Moses (and subsequently Joshua), by the High Priest, i.e. Eleazar, and by the lay leaders, i.e. the princes. Each one of these leaders possessed an exclusive authority. Maimonides wrote in chapter four section ten of his treatise Hilchot Melachim that when a (Jewish) king conquers a country the whole country becomes legally his, and he can dispose of it to his servants as he sees fit. This shows that the king has overriding authority. As far as the princes are concerned, they enter the picture when the king wants to share out to every one of his people a fair share of the spoils. In such a situation all the representatives of the people, i.e. the princes, need to be present and arrive at an agreed formula at the time the shares are handed out. The function of the High Priest was to inform the people where their respective shares were located. In other words, the king might have decreed for everyone to receive 100 acres of land but did not say who was to get which parcel of 100 acres. You will note that each one of these three authorities had to contribute his opinion in order for the distribution to take place without friction. Furthermore, inasmuch as the function of the king could only be fulfilled after he had conquered the land and the people were settled therein but not at the beginning of the whole process of conquest, it certainly would not have been sufficient for the tribes of Reuven and Gad to submit their claim only to Moses for his adjudication. The word לאמור may mean that the princes were to convey the claim of Gad and Reuven to the people at large in order to secure their approval also. Alternatively, the word emphasises that their claim was presented in "soft language," i.e. אמירה; they were not aggressive in the manner in which they presented their request.