HClass12

I had 3 budgies to start with 2 males and one female. I recently rescued 4 from my college that were going to be put down if no one adopted them. I brought home two males and two females. My original male name Chester keeps picking on a new male that's only about 6 weeks old. Chester has already sent the new male named toby to the vet because he couldn't walk. And Chester seems to have bonded with one of the females we have so I'm not sure if he's jealous or territorial or whats going on but I'd like to prevent having another huge vet bill.