How can I get these dogs to stop being so wild?

My girlfriend has two dogs, Lucille and Brenda. These are the biggest, dumbest dogs in existence. They are spayed females, German Shepherd mix, two years old, and sisters from the same litter. They are too much for my girlfriend to walk, so it is my job to walk these beasts. Every time I get their leashes to take them for a walk they hear the clinking of the leashes and charge me. I'm tall, but thin, and these dogs are so excited that they jump on me and knock me down. Every time. I tell them "No! Bad dogs!" in a stern voice, but they ignore me and tackle. Walking them is no fun, either. They are curious about everything and if they see, say, a flower in a yard that interests them, they just drag me along with them while they check it out. Taking them to the dog park is a nightmare. I have to fight to get them to come home. My girlfriend thinks this is cute. She'll say to them "Oh, did Daddy take you for a nice walk?!" Meanwhile, Daddy is beat and cussing out the dogs.