Since she doesn't formally have the title of Lady of DunDealan, Merida will be unaffected and available for brain picking and/or curing people she knows and loves. Watching your father and boyfriend turn silver is bound to be terrifying :'D that said! she's willing to be touchy feely with people she knows and loves

Terra will be reenacting the ending of Frozen with Aqua but will otherwise want to help in any way he can! He has a couple of Potions which he can try out, or you can drag him to the Caer Glaem library for research or w/e