One moving-coil mic for two flutes will be.... challenging, to say the least. Something with a wider pickup pattern, like a Sennheiser 421, might work, but I can't imagine it being preferable to using two mics. An SM58 on each flautist would work fine.
A good multipattern condenser would open your options up tremendously. AKG C414, Austrian OC818, Neumann TLM107, something like that. A single of any of those would be useable on two flutes for sure.
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As someone that plays classical flute for wedding ceremonies, using one mic for two flutes is not ideal.
My trio (F,Vi,C) has done many outdoor "concert-in-the-park" performances that require sound re-enforcement..
My favorite mic to use is my Senn 421. It seems to draw-out the low register of my flute really well.
The 421 is rather big & in the way, so I usually just go with a Senn 835 (with windscreen) and call it a day.
What I have found to be the best position for a mic (on a flute) is 6-10" in front of the lip plate.
Adding a windscreen will cut down on the bit of air that passes over the air-reed.
If I were to attempt to cover two individual flutes with one mic I would use one of my choral mics: Shure MX202B/C
Getting back to weddings: playing flute "acoustic" works for me .....
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