How did the Pool of Knowledge and Font of Power affect the Daughter and the Son?

Are they actually what gave them power in the first place, or did it just amplify what already existed/give them knowledge to go with their power? If so, how did the Father become so powerful, and what powers did the Celestials actually have?

They were already all-powerful Celestials. FOTJ notes they were "unaffected" by the Pool and Font, though it turned them into embodiments of the light and dark.

The arguably-soon-to-be-Legends-canon source Supernatural Encounters expands on this:

On a hidden world, a pocket dimension between realspace and the realm Beyond Shadows, the Celestials created the Wellspring of Balance, from which Elegast incarnated into mortal form. From the Font of Power was incarnated Eipha, who became known as the Son, and from the Pool of Knowledge was incarnated Niphal, who became known as the Daughter...

The Wellspring of Balance, the Font of Power, and the Pool of Knowledge were maintained to ensure that he and his offspring would, in mortal bodies, remain alive over the ages, for although time passed differently on their world, still it passed. Yet those very same waters would prove volatile to Eipha and Niphal, with the Son gravitating towards the Font of Power in order to regain his physical strength, and Niphal the Pool of Knowledge in order to regain her mental energy, both of which were drained by the galactic imbalance. But in this way did it escalate and intensify the differences between them, so that in time, they become as avatars of Darkness and Light, and like the galaxy itself, never truly able to become whole or one.
 
Their natures now so opposed, Son and Daughter frequently fought amongst themselves, and in their most contentious battle, they accidentally destroyed the Wellspring of Balance. Despite their animosity, they loved one another and longed to be together. Father strived incessantly, but without the Wellspring, he soon grew weary in his task and was unable to restore the balance in himself. In this way did a deep loneliness set in, and he began to regret having coming to this plane.

Interesting. So the two nexuses acted like Lazarus Pits, preserving the physical form and restoring it whenever it was weakened when the balance of the Force shifted?