It sounds like the one year old is bullying the pup and you need to take control. As soon as he is too hard on the pup, it is time out for 5 minutes. Does this teenager get enough exercise and training with you? Seems like a big project.
If you let this go, it can make the pup dog aggressive.
Deja, GSD, sable WL, female, born 11 / 2013
Cam, Rough Collie, sable, male, born 8/2015