I would say rewards is the biggest key to start.
Give them something small like a sticker on a chart each time they just "sit" on the potty. After so many, they get a prize at the end of each week.
Then, once they are doing that consistantly, do the same each time they do their business in the potty.
Before long, you will have two potty trained girls.
Also, make sure you get them potty training underwear and call them "big girl pants." Little girls look up to older girls, so this usually helps to be called a big girl.
And just to let you know, there are books out on the market that you can read to kids (two versions, one for boys and one for girls) that you can buy and read to your children when they are trying to learn to use the potty. Check with your local bookstore or library for specific titles. I used to have one, but don't remember the name of it.
Another key they said on Ophra was to watch your timing.
Like taking them to the potty periodically, example: Shortly after meal time and watching for signs from your child.
Good luck!