What can I do to to help my dogs?

I have three dogs. the first one is a chiwawa mix and she came from an animal shelter and she was around 4 yrs old when i got her. (shes now around 5 probly). the second dog is a yorkie poo and he is now a year old. I got him when he was about 8 weeks. Lilly ( chi mix) and jack (yorkiepoo) got along great with each other on day one and they still do. I got them both when my husband deployed overseas. He is back now and we decided to get another dog. We just got Clyde. He is an 8 week old german shepard. He came from the animal shelter also. Lilly and Clyde get along with no problems but jack does not like Clyde. He has attacked him several times over a toy, over me, or sometimes for no apparent reason. It scares me and i panick and i try to stay calm but im really scared they are gonna hurt one another. Jack gets along with my moms two dogs with no problem. So i dont know what the deal is with our new dog. I tried introducing them to show them that its okay, i took all the toyss up so they wouldnt be able to fight over them and that still hasnt worked. i need advice or tips on what to do. please help. thank you!