Congratulations on your latest arrival!
Your new boy Ozzie is a gorgeous cobalt violet single factor golden face spangle budgie.
When bringing home a new pet bird, it's always best to follow quarantine procedures before introducing the new bird into the flock.
This is done as a preventative measure in case the new bird is carrying a potential illness that can be spread to the existing flock.
Even though your budgies have already met, you can still quarantine Ozzie.
You can find detailed information on this link: https://talkbudgies.com/new-budgie-ar...necessary.html
As for Ozzie being more quiet, he is still in the process of settling in to his new home and it takes time for him to feel fully comfortable. You can help Ozzie by covering his cage on 3 sides (leaving front part uncovered) and having some background music on for him. The music or background sound from the television will likely encourage Ozzie to sing.
Best of luck with your new little friend!