you can learn in chapter3 skills only up to lvl3. you need to learn huldra4 from hilder in chapter4 after getting to the alpines and before driving to alfheimr.
as seidr you need to use the units from last row in your fights, to use potions in hard fights (i use valhalla for every fight as seidr), and luck to get griffin->wolf and aurora->hildr combos.