How long of rush practice are you having? Offer breaks during practice to keep people into what you're doing, but also to have a break. Also, let the sisters know that the faster you get through everything, the faster rush practice goes.
Well, as for having folks stop talking and show up on time, instead of things like fines and punishments for not doing it, have some sort of reward in the end, like say, for the sister who goes to every practice and is on time every practice and participates and such gets a gift certificate to a local restaurant or a sorority t-shirt or something. The best advice here is to reward good behavior. Punishment and fines only end up causing animosity.
As for having sisters talk to sisters they don't hang out with, do a secret sister or rush buddy thing. Instead of letting people pick here, have everyone put their names in a hat, and pick a secret rush buddy who they can get little presents for and provide an outlet to bitch
Don't worry, you'll be GREAT!