Actually, those cores aren't the exact recommended ones anymore, they just haven't been changed. Bsnes Balanced for SNES. Nestopia works great as well as FCEUMM, so either works. N64 emulation isn't the greatest either way, and the new core for that isn't ready to go just yet.
You also need to make sure like @In virtute Dei said, that the core is downloaded, but the name here on the associated platforms page and on the left of LaunchBox match, RetroArch is linked properly in RetroArch (more when updating). He posted the video tutorial that will probably help the most.
I'll also move this thread.