7 vocals and 7 instruments....that'll move a lot of air.
IME, stage volume is under the control of the drummer. Why are they wailing? Can't hear themselves? Maybe a better monitor system is needed.
Especially if you have two wailing drummers. IMO, I'd start there. At rehearsal, have them play very softly for an entire song and bring in each instrument one at a time to make sure each one can be heard.
Slotting all the instruments at different freq. ranges, tones and playing full chords, partial chords, especially the keyboard needs to be "studied" instrument by instrument so that the FOH mix will sound balanced. Maybe you have too many chord instruments playing on top of each other along with too many vocalists.
As far as 7 vocalists, seems like overkill to me unless you have the rest of the band under control and each vocalist add something unique to the tune. Possibly use lest vocalists per song? Or maybe if you had only one of each instrument and only 3-4 vocalist singer per song, your band would be easier to manage sound/stage/gig wise and you might actually sound better.
Recording/studying your rehearsals may lead you in the right direction.
Here are a few links to check out:
Frequency ranges of band instruments Bass string notes,frequencies and harmonics chart EQ primer (all instruments) FOH vs. on-stage sound