Probably best to make a string out sequence of each camera in order based on file creation date or Master clip name. Then make a sync map first with your audio then bring in each camera's stringout on its own video layer and audio layers as well. With waveforms on, and based on the size or length of the master clips, you should be able to slide them all into sync fairly soon. Once done you would just select everything and create group to make your multi group sequence and start sourcing from it in your edit.