en_tn_lite_do_not_use/jos/18/04.md

the land up and down

The words "up and down" mean in every direction. Alternate translation: "the land in every direction" or "throughout the land" (See: rc://en/ta/man/translate/figs-idiom)

write out a description of it with a view to their inheritances

This means that they will describe the portions of land that each tribe would like to receive for an inheritance.

their inheritances

The land that they are to survey is spoken of as if it were an inheritance that each of the tribes would receive as a permanent possession. (See: rc://en/ta/man/translate/figs-metaphor)