At least double system will be relatively simple as even though you are changing frame rate on one of the formats, it won’t change real time if it is via pulldown.
Are the audio files in broadcast wav format by any chance? If so they will have embedded timecode which is likely to cause problems if you are changing rate to something different from the audio files. Did they shoot with a timecode slate or lock codes to the 29.97 camera?
One fix is to convert the files to aif first. This is quick and won’t change quality, just get rid of the metadata. Import those files into the sequence once you have made the decision about frame rates etc.