I had a variety of pictures, videos, pdf, basically every file on my usb and my brother formatted it for a xbox 360 and installed files from xbox, is it possible to get these back at all?
Very unlikely to get data after the usb has files installed from Xbox 360. The newly installed files must have overwritten previous files making recovery process dicey.
However, you can try downloading data recovery software and scan usb drive and see if you can get your old files..