Dragon Seer Series by Janet McNaughton

Enslaved since early childhood, Madoca 14 is surprised when dragon chooses her for newest dragon seer, to learn lore from Orkney dragons. People forget the importance of dragons. Nightmares come true when Vikings arrive to plunder with a malevolent seer who wants dragons killed. Can her emerging wild powers send beloved dragons to safety?

Bored by homework and bullied at school, twelve-year-old Gwyn Rae reluctantly takes on a Heritage Fair project to boost his history mark. He begins to investigate the papers of his ancestor, Daniel Rae, with help from his older sister, Maddie. Together they discover a notebook filled with writing only they can see and an iron key that seems to react to their touch. When the key unlocks a secret door in an old church, Gwyn and Maddie are launched into the adventure of their lives.