It was actually confirmed that Iduna and Agnarr are the same people as Tarzan's parents, this was confirmed by the director, and he also stated that during the voyage, the queen was pregnant and the voyage was longer than we thought... Honestly, I'm surprised I'm the first person to make this discussion.
Chris Buck said they were connected in his "fun little world", because he directed both Frozen and Tarzan. He also tied in Surf's Up, another movie he directed. I doubt there's any genuine connection between the two. There's too much evidence that contradicts it. for example the ship in Tarzan went down in flames; the ship in Frozen didn't.
I saw the side-by-side photos of both sets of parents. They look nothing like each other. The King has strawberry blonde hair and a moustache where as Tarzan's father has dark brown hair, a moustache and sideburns. The Queen has dark brown hair where as Tarzan's mother has red hair.