Advices on aggressive chin

My older chin Silver is just one-year-old male; I was thinking to find him another chin as a company, and I found one 3-month-old male from local breeder. But before I went to pick up the new chin, I travelled for 5 days and left enough food and water for silver. He was 720g at the time I left, and weigh down to 700g when I came home, he’s obvious not happy for me leaving so long. I picked up the new chin on my way back home, and put him into a separate cage for quarantine. The new chin is doing well and I put his cage next to silver’s cage to let them get familiar with each other, he’s still a baby and very friendly to silver. But silver is very aggressive, he dumped up and down in his cage, even tried to bite the new chin across the cage (I left enough room so he won’t get to bite the new one). He’s also very nervous these days, he didn’t eat as much, his poops are normal though, but his weight didn’t gain back and is around 695g now. He tried to search the new chin even when I put the cage far away. I did researches on introducing two chins, and I understand it might take months, but I'm worried about silver now. Should I still keep their cages next to each other? Is this normal that the old chin get stressed by a new chin?