Wow BA - that's awesome! Congrats to you & GF! I think it's great that your girls are onboard. But teen girls do not like sharing their space as a rule. Maybe having all the girls help plan their room arrangements/decor would make a negative into a positive. IKEA has some great storage solutions. Maybe there would be room to add a tall armoire for more clothing space? But since they are both in college - maybe it won't be so much of a problem.
At any rate - I'm sure it will all work out & I wish you all the best.