sorry for the late reply, having issues with my tablet atm
1. Ophelia's main goal is Fal, she later learn that not all demons are bad, just like not all humans are good and accepts that fact.
2. The terms of the Pact Ces made with Ophelia is that as long as she keeps Ces entertained, she will live forever. Ophelia doesn't exactly trust Ces so at first she rejects Ces's offer, only when she is about to die and her kingdom's in danger of being destroyed does she accept his offer.
A. Its not really Ophelia's soul that Ces controls its more like the hourglass of her life, however Ces does turn Ophelia into a half breed, so she does have certain powers and is more stronger than she was before.
3. There are some things I can't say but Fal doesn't see his actions as evil.
A. You could say he is evil from the start he just wasn't open with it, its a mystery on why he decided to do all of this.
B. Fal needs 4 bodies of the royal bloodline to open a small portal to Agi, the demon half of the world. Lia's(Ophelia's Mother) parents are already dead from natural causes so nothing really needed to be done with them. Fal needed 2 more so he killed both Ophelia's mother and father, he poisoned the Mothers food, and killed the Father when he found out what Fal was doing. so its safe to say Fal will stop at nothing to bring the worlds back together..
4. There are 2 Goddesses, Nurus, the Creator of humans and Agi, The creator of Demons.
The functions of the two goddesses where to watch over their creations and keep balance between them, however their plan didn't work and they decided to split the world apart. Currently they reside in Temples not reachable by normal means, you would have to fly there to reach it.