Complex sentence: In addition, the IFCC have already involved themselves with the quest for the Gates, having sent Sabine to accompany Nale, and that they consider the Linear Guild their pawns in the Gates quest.
Split into simpler sentences: In addition, the IFCC have already involved themselves with the quest for the Gates. It is revealed that they are the ones who sent Sabine to Nale, and that they consider the Linear Guild their pawns in the aforementioned Gates quest.