You’ll definitely want to read in the FCP manuals, but:
1) create a new timeline with 6 channels of discreet audio (under User Prefs, Audio outputs). Copy/Paste your video clips into this.
2) get 6 discreet mono aiff/waves from your audio mixer. So a Left Front, Right Front, LFE, etc….
3) these go into your timeline. Typically 1/2=front, 3=center, 4=subwoofer, 5/6=rear speakers
4) you’re probably editing on a stereo only system? to hear channels beyond track 1/2, you’ll need to use the Stero Mixdown switch in the Audio Mixer
5) edit away.
6) export each track as a discreet aiff and compressor can make a 5.1 dobly digital file from a “surround group” Look this up, it’s pretty easy once you get the hang
IMHO, I would avoid trying to do anything fancy with your interviews. Just mix all that audio down and put it in the Center channel. I’ve heard that they typically mix 15-20% of the center channel into the Front’s. But I’m not an audio mixer and prefer letting them do their magic instead of me.