If you're talking the original Apple ][ or the Apple ][+, then no, it couldn't display EGA-quality graphics, but since the Apple //e with 80-column card (had to be at least a Revision B motherboard too), had a double hi-res graphics mode with 560 x 192 pixel resolution (in black and white) and 140 x 192 resolution in full 16-color glory. King's Quest on the Apple //e and later used DHR mode, and looked just the same as on a PC with 16 color EGA graphics.

The Apple IIgs with it's 320 x 200 pixel super hi-res screen could do King's Quest the same as on the PC too.

And yes, if you can find a copy of the Sierra Interpreter with a version number greater than or equal to the one that I assume the Brothers Chaps are using, then you can take the data files and interchange them, and run them on something other than a PC. The only thing is that the music may not sound the way they intend it to, because for each platform Sierra customized the interpreter's music capabilities to match the platform's music capabilities.

For example, I tried using the data files from a fan-made game written for the PC interpreter that had music, on the Apple IIgs using the interpreter from the IIgs version of King's Quest III. The "game" (if you could call it that... it looks like the author got tired of it after designing three screens) played perfectly. The music did not sound right, as on the IIgs, Sierra took advantage of the computer's built-in Ensoniq 8-bit synthesizer chip and used crude wavetable instrument sounds instead of just beeping at different pitches.

In fact, if this is what the Brothers Chaps are doing, and if an open-source type interpreter won't work to play the game on a Mac, then you can download one of the IIgs emulators available and play it using one of the Sierra AGI game interpreters there, as long as you're willing to compromise on the music.

Or, you can use Virtual PC to play the game. It will run quite acceptably well. Just make sure you use Windows 98 or earlier (Windows 95 or DOS is preferred). Though I haven't tried, DOSBox may work too (you REALLY don't need a speed demon).