“across, yes, across.” This is the figure of speech polyptoton for emphasis (see commentary on Gen. 2:16).
“this people.” This seems to be poor English grammar (we would say “these people”) but the Hebrew is singular, “this,” here again pointing out that God considered Israel to be a single people, not a collection of independent persons.
“into the hand of the Amorites.” Joshua knew that the people in the hill country of Judah, Benjamin and Ephraim were Amorites. He had acute political awareness.
“to destroy us?” Here Joshua is very honest and frank in his prayer, as we should be.