# their brothers

"their fellow Israelites" or "their relatives"

# Come up with us

"Come with us" or "Go with us". The people of the tribes of Judah and Simeon were camped in the valley of the Jordan River. The land given to Judah was in the hills above the valley. 

# that was assigned to us ... that was assigned to you

"that Yahweh assigned to us ... that Yahweh assigned to you"

# We in turn will go with you

"In the same way, we will go with you"