Board Thread:General Discussion/@comment-25081838-20150101013328/@comment-24674051-20150102182909

Honestly, I don't think we know for certain how this is all going to play out. We know we have Ursula, and we are getting Posiedon. I have not seen anything confirming how the Under the Sea characters are going to be related, or if they are going to be related. A lot of it is rumor and supposition based on what we know from outside works (ie the Little Mermaid movies from Disney).

We also know that, at least in Eric's kingdom, Ursula was regarded as a Godess, and even Ariel mentioned her as a Godess that has not been seen in a thousand years.

Now, if I were to guess based on what is confirmed above, my guess is that Posiedon is Ursula's father. Since nothing has been said about Triton, or Ariel's family, we can't assume that she is in any way related to Posiedon. She could simply be a mermaid that happens to like humans (much more than the other mermaids that would just as soon kill a human).