The extent of a seer's gift is they cannot call upon visions, but they receive them randomly, and they don't always come true. Visions often only come to seers about themselves, or people they've met.
Differences from humans: they are stronger, faster, heal more quickly, age more slowly. They also have faster metabolisms, requiring them to consume more food, etc.
Limited Fire manipulation: They can't start fires, but they can't control them once they're lit.
Mild poison resistance
Slowed aging: Once demons are fully grown, their aging slows by half. Humans age twice as quickly as they do. Demons also are likely to live to be much older.
Weaknesses: Holy Magic, which has been lost along with the angels.
They have similar powers to demons, just not as strong/powerful.