Use a bunk bed with a trundle bed underneath so you can roll the bed out at night for the girls to sleep. Then you can tuck it back under in the morning. This only takes up the space of one twin bed in the room during the day, because the beds are all stacked together.
Situate three twin beds side by side in the room with just enough room between them to walk. Use a slim nightstand between each bed as a guide to how far apart to place the beds. Add storage by putting a trunk at the foot of the bed or opting for bed frames that have a drawer that pulls out from the foot of the bed.
Set a bunk bed on one side of the room and put a third, twin bed across from it. Use the space in the middle for a dresser or nightstand. Use the space underneath the beds for extra storage by getting captain's beds or shallow storage containers.