You can certainly train Maya to nip less, but puppies do nip a lot. It will definitely get better eventually, as she gets older. We got Pixie at 8w, and I have a 7yo, so I've been through the same thing. She's 8m now, and the nipping is much, much less. She'll rear up and mouth my hand when she wants to play, or when we start out on a walk (because she's so excited). My son will get her riled up and she'll nip then, but she saves most of it for playing with other dogs these days. Also, her puppy teeth fell out at 5m - the adult teeth aren't nearly as sharp!
Maya undoubtedly sees the girls as littermates, rather than as above her in the pack order. You can read up on how dogs establish pack order, it will give you ideas to try at home. One thing I can think of is, when you are all going outside, always make Maya the last one through the door. Make sure you and the girls go out ahead of her.
When Pixie was nipping a lot, sometimes I would grab her muzzle, give it a quick shake, and say sternly, 'NO BITING'. When she licked our hands, we would give her tons of praise and attention, and say 'good kisses!' over and over. Sometimes I would withdraw my hand and offer her a toy to chew on instead.
Pixie still jumps and play-bites with our son. He knows what to do to discourage it, but he likes to play that way with her, so he encourages it. Of course, he occasionally gets mad when she nips too hard, but I remind him that she's just a pup, and doesn't mean to hurt him. If your girls don't want to play that way, obedience training will really help. Sometimes you can find a trainer to come to your home, or you can bring the girls with you to the class and ask the trainer to help you figure out how to discourage the jumping and biting. You'll have to train her for the Down command to help with the jumping. You can also have the trainer show you how to put Maya in a submissive position. I do this occasionally when Pixie gets too excited, to help her calm down. It's good to do this on a daily basis for a while with puppies, too.