Sometimes is needed to makes music score for a flute ensemble and we don't have the basic knowledge, it's not to hard like as seem, I'll explain to you how to write music for a flutes quartet.
1.- the firts thing you have to know is the distribution, the melody is use to be in the firts voice, the octaves of this voice most to be in the high level of the flute sound, the second voice goes third down, the third voice goes a third down from the second, and the four goes a third or five down from the third.
2.- you can use choral music to transcribe to the flutes, in this case the firts voice is equal like a soprano, the second is a contralto, the third is a tenor and the last one, the four is the bass. you may need to fix the keys of the piece becouse sometimes the register of voices ara not like the flutes register, and need adaptations, so you have to be carefull, the firts flute or voice don't needed to be to high, and the four flute don't need to be much bass,
3.- The music from a string quartet, always represent a good option too, and the piano score. but have to be carefully about this, and change keys or register of notes if are necessary.
4.- About the level of the flutist is recomende put the most avanced in the firts and second voices, the medium, initiation and basic level in the third and four flutes.
The diferents levels of playing may be together, but the conductor of the group ensamble most have to distribute as better as it can