Silver Princess Series by Sharon Green

Princess Alexia is the most accomplished shapeshifter on Golran, but when her father calls together the most able shapeshifters in the kingdom to compete for her hand, she vows to best them all.

Shape-shifters Alexia and Tiran, and magicians Chalaine and Bariden, must pool their occult powers to liberate their empires from the evil usurpers who have plunged the realms into chaos and despair.

Taking their rightful places as rulers of the land, shapeshifter Queen Alexia and warrior champion King Tiran are confronted by a terrible sorcerer who enchants the queen and threatens to enslave the kingdom.