‘ And the children of Israel did so, as Joshua commanded, and took up twelve stones out of the midst of Jordan as YHWH spoke to Joshua, in accordance with the number of the tribes of the children of Israel, and they carried them over with them to the place where they lodged and set them down there.'
This was what they had been commanded to do and this was what they did. The overall stress is that they were obedient to what YHWH commanded. They took up twelve stones from the bed of the river, one for each of the tribes of Israel, and carried them to the place where they lodged that night.
Notice the stress that all Israel was involved in the act of the twelve men. The men did it as their representatives, but it was all Israel who were doing it. This was stressed by the plural ‘you' in Joshua 4:2, and now here.