We have mandatory study hours for everyone and no one gets anything done. I like the idea of a study log in the lib or for the sister to take. Maybe your house should focus on rewards and points board. Girls like rewards. I can not study with my sisters, i fool around and distract everyone, i need to be in a lib. with a more academic setting than our living room/dinning room.
Good Luck I don't think I helped a ton, but you'll get through it! Focus on rewards!
Tau Love