Do the mikes have to be out of shot? You could have two pairs of talent share a wired handheld mike on stands. You could have all four on lavs wired to
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Unless you plan this kind a shoot on a steady basis it might be cheaper to hire an audio tech with his/her own gear. Riding four channels of audio while also shooting is really hard. Speaking of which, how do you plan to shoot this? One camera on a wide shot? I suppose if it's just a wide shot you can ride the levels. If it's a multi-cam production, I can't see riding audio levels and switching. If even one camera moves and reframes on the fly, no way can you also ride audio levels.
You'll get more bang for your buck with wired lavs than wireless. Plus you might run into locations where the wireless has interference. Audio techs always have wired backups in case. You can add the wireless kits later.
If you do float mikes on stands above the talent, say two mikes between each pair then you need to train them to keep their heads pointed in the direction of the mikes. It won't be ideal but you will hear the dialog. You can adjust the levels in post but at the price of quality.
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