I would like this all to be true because I love when the Disney movies connect, but there are some things I can't ignore:
-Tangled: Yes, I believe that one is true because we see a brief glimpse of Rapunzel at Elsa's coronation, so it probably means the families knew each other and Elsa's parents could have been traveling to Rapunzel's wedding when they met their demise. So Frozen and Tangled connection: check.
-The Little Mermaid: The ship Ariel explores could have been the King and Queen's ship, I've seen that theory, but I wonder if it could have belonged to Tarzan's parents too (which would be the same ship according to the theory you mentioned). There's nothing on the ship to confirm who was traveling on it, so guessing the owners is a stretch, BUT it could have been the King and Queen's, sure.
-Tarzan- NOW, this is the one I'm always uncertain of, because certain things don't add up. Tarzan's parents don't look like the King and Queen and they are not dressed in that kind of garb. Alright, I'll let it go though. Maybe they weren't dressing in royal clothes until they got closer to where they were going. They look nothing alike, but ok, I'll sweep that under the rug. It's Tarzan's birth that is the uncertainty here. If I recall correctly, Elsa's parents told her that they would be gone for two weeks. The Queen does not look pregnant when she leaves, but ok, maybe she's two months or something (if pregnant at all at that time).
I can't tell the age of baby Tarzan when we see him for the first time in the rescue boat, but even if he was a newborn, the King and Queen's ship would have had to go missing for at least about seven months (if the Queen was pregnant when she left, longer if she wasn't). So, we have to believe a ship that was supposed to be gone for two weeks, got lost and somehow had enough supplies for months? Yeah, they could have fished for food so they didn't starve, but another question is what happened to the crew? The King and Queen would have probably had a lot of royal guards and crew with them, would they all have just died in the fire on the ship? Tarzan's family probably had a crew too that perished, but maybe not one as extensive as I would imagine a King and Queen's to be.
Lastly, Tarzan's parent's ship is on fire and then it sinks. The King and Queen's ship is shown to be just swallowed up by a wave with no fire in sight.
The co-director of Tarzan and Frozen may have wanted Tarzan to be the younger brother of Elsa and Anna, but he didn't make Frozen in a way that would make that theory believable, in my opinion anyway.
