I have two female Jack Russell terriers both 8 weeks old ?

I have had one of them for close to a week and the other I got two days ago.The second girl aggressively attacks the one that I had first..Won't allow it to eat..play with toys..drink..play with her.The growly by her is very loud and sounds extremely vicious..anyone help me.I am thinking of taking the second one back to the owner..May not get my money back though...He gave me a written guarantee for 72 hours but only for health issues...Please don't poop on me only answer if you have something productive to say..Thank you. I don't feel much like being attacked today.