If you want the truth... (SPOILER)
It's mostly hinted that Vaan and Penelo are an item and even more debatedly the pairing of Fran and Balthier... But you never get a scene where you see the pairs declare their love or start smooching. In that sense the characters could also be percieved to be just good friends.
Vaan and Penelo though do have stronger hints to being in an relationship. A few of the NPC's in Rabanastre allude to the fact that the two at least have crushes on each other.
As for Fran and Balthier, it's more difficult to say. But there is a huge... thread dedicated to that subject.