Two German Shepherds not getting along!?

I have a 7 year old gsd, Sheba, and now a 4 month old gsd named Niko. I've had Niko since he was 8 weeks old, and since the first day he arrived the two dogs have been mean to each other. Niko's been pretty good to Sheba, but the older one is usually the one who starts the quarrels. She won't let him near her food bowl, her toys, and even me! She even leaps at him when he steps into the same room as her. Growling, barking, running, pouncing, and biting makes it very stressful in our home, especially with a 5 year old boy on our hands, too. HELP!