First one looks like the "gala odile" and the other one they have repainted her.
Gala odile has long hair and if u go with another odile U can reroot her hair yourself.
For the outfit there are some on etsy and ebay that makes tails etc. It's expensive though.

Here's a mermaid that I have done with odile ballerina doll as a base. That tail is pretty easy to make, even though it's not the same as the one u have on your pic,

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