Audio Syncing/Multiclip Issues in FCP 7

Hi Group. My first post here so forgive any breaches of protocol or silly questions.

I'm a fairly new FCP 7 editor, working on a project with several three-camera interview shoots. In one case (for reasons beyond me) the audio off the three ISO cams is crackly and useless. A fourth file which was created in the studio with live switching from the three cameras, has the only quality audio track.

I'm an assistant on this project, and need to be able to work on the edit, then hand them back to the main editor (who is off on his honeymoon now!) I want to be able to edit the interview from the three ISOs, but using the one good audio source from that "pre-switched" file. All the shots are in XDCAM codec.

Plan 1) I thought I would simply create a multiclip of the four files, then edit it using the good audio track.

Problem is: that file with the good audio track is in 1920x1080 whereas the ISO shots are all 1440x1080. (I believe this has to do with square vs rectangular pixels.) In any case, FCP won't let me multiclip them.

Plan 2) I pulled the good audio tracks from the 'switched' interview into the browser, and tried syncing them (sans video) with the three ISO shots in a multiclip. This worked... however, despite my sync points being right on the same audio beat, the audio winds up totally off.

I don't understand this part, but might be because the "good" audio track has a different audio bit rate from the others: It is 24, vs. 16 for the others. Would this cause slippage or problems in syncing in a multiclip? They are all at 48 khz.

Plan 3) Since I couldn't get multiclip to work properly, I just manually laid all the video tracks in the timeline without the crummy audio, synced them with the good audio shot. I am trying to cut this way, but it is very laborious. I get massive render times due to the different frame sizes (or maybe different audio and data bit rates too?).

It would be SO much easier to cut this from a multiclip!

I'm open to any suggestions. I am a bit wary of converting the files. In the past I've worked in ProRes422, but I'm not sure of the current ed's preference. Even if I converted the 1920 frame to 1440 (or vice versa), I worry the multiclip audio slippage may continue. Would converting the 24 bit rate audio to 16 fix that issue? I'm not sure.

There are so many things I can try... I'm not really sure where to start. Which is why I'm looking to this forum for some guidance.

Thanks for your patience and your help.

Ben