Queen Iduna and King Agnarr. Also, for those that read the person who said Elsa and Rapunzel are sisters, they are not. Elsa and Anna are sisters. Rapunzel is their cousin. It has been confirmed by Disney and the writers of Frozen. Tarzan is their little brother, AND it is their sunken ship that Ariel explores.
The names on the tombstone especially translate to Agdar and Idun, but when they started appearing on more of the merchandise, their names were changed to their more Anglicized forms, Agnarr and Iduna.
elsa and anna are not sisters, elsa's mother and father are the king and queen of corona (where tangled takes place) and elsa is twin sisters with rapunzel. the mother and father of anna are agdar and iduna.