“beyond the Jordan.” That is, beyond the Jordan River. Maps in the western world have north at the top, and we westerners orient to the north. That was not true in biblical times: people oriented to the east, where the sun rose. The Old Testament is focused on the Promised Land, Israel, and if you are in the Promised Land and look east, the land God gave to the tribes of Reuben, Gad, and half of Manasseh is to the east and “beyond the Jordan River.” So the land east of the Jordan was called the land beyond the river, even if you were standing on it, as these men were.
Some scholars see this as evidence of a later author or reviser who wrote from the perspective of being on the west side of the Jordan, but that is unnecessary. The people of Israel knew their inheritance was west of Jordan, so they could already speak of the “other side of the Jordan” as land that was east of the river. Furthermore, the geography is clarified in Joshua 1:15.
“before your brothers.” The Hebrew can mean “ahead of,” or it can mean in such a way as your brother Israelites can see them, “in the presence of” the other Israelites. It could well have both meanings here.