Here "firstborn" and "younger" are nominal adjectives that refer to Lot's two daughters according to their birth order. AT: "Lot's first daughter ... Lot's last daughter" or "The older daughter ... the younger daughter" (See: [[rc://en/ta/man/translate/figs-nominaladj]])
It can be made explicit that their goal was to get him drunk. AT: "drink wine until he gets drunk" or "get drunk with wine" (See: [[rc://en/ta/man/translate/figs-explicit]])
This speaks about giving Lot descendants as if his family were a line that they are making longer. AT: "so that we can bear children who will be our father's descendants" (See: [[rc://en/ta/man/translate/figs-metaphor]])