Quick question

If i have a work that includes 3 flutes, and i want to write the parts on the same stave, how do i properly indicate that i want all to play the one notated part, or a certain two to play two notated parts?

It's a bad idea to have more than 2 instruments on a single staff. Once they break into harmony, it's very difficult for the performers to read. It also severely restricts how independent your parts can be (and therefore how interesting you can make them).

But, if you must... If you want all three players to play the same part, mark a3. If you want individual players to play, indicate either Fl.1, Fl.2, or Fl.3.

N.B.: This only applies to wind instruments. Strings are a different animal.

Thanks. In case your interested, this question refers to my March from Spanish Concerto. Thanks, thanks, thanks.