Flatfoot - there's a common thread in the previous posts and I'll pile on - you likely need to do some hi-pass EQ on all of the vocals. Where you do the cutoff frequency depends on the voice, but you'll likely find jcspro and rharv's starting points as an 'aha' moment. And, just plain cut down on the volume of the BGVs can do wonders AFTER you've done the eq on them.

Hi pass filtering is probably the most neglected tool in the home recordist's toolbelt, that can make the most difference in un-muddying a mix.

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