NPAPI is for NPAPI-based browsers (e.g. Firefox and Safari).
PPAPI is for Chromium-based browsers (e.g. Operat).
As for packaging them together, we've not done that, nor tested it. It's an unsupported scenario. If you do that, it may or may not work. The installers do write to some of the same files, depending how the installations occurs, they may stomp on each other.