Mixing formats

I am editing using footage from a Sony EX3 and a Sony Z5 - what should my audio-visual settings be to optimise export quality? Is there a conflict here and what do I do to avoid it? Presumably the Export should be through QT Conversion, but what should the settings be here to maintain 16:9 aspect ratio - at present the image is squeezed - 16:9 including black letter box? Thanks

Use Compressor to convert the media in a single format using ProRes and edit in a sequence that matches it.

All the best,

Tom