Mermaid Help

The reason they are still swimming with their legs and not their tails is because they have not been outed, or think they have been outed as a mermaid. EA did it this way so for those who want this pack but don't want the occult life state to be "up in your face" type of thing. If you can find one of those large conch shells to blow through. Blow it around the mermaid and they will do a dolphin type of cry, and do something odd with their hands. That is the fastest way to expose them. After doing that, there will be an option to ask them about their odd behavior, or something like that.

There are two things I know of that can make Merfolk premades & game created townies show their true form in Sulani. One of them does involve the "ordinary' seashell. You were close, but there has to be Merfolk on the lot or close to it when your Sim blows the call. If there is Merfolk nearby, they'll come over and do their little derpy dance and dolphin sound. After that happens, your Sim can ask them why they did that. It's in the socials somewhere, just click on them and look for it.

They'll say something about it being something they do to show respect for their people, it's their song and admit to being Merfolk. After that, next time you see this Mermaid/Merman (or any Merfolk) in the water, they'll have a tail and swim the way they should as Merfolk.

The other way is one of your currently played Sims must be a Merfolk, either created that way or by eating one Mermadic kelp. Mermadic kelp can sometimes be found in the cave with the graffiti next to it. Or if your Sims have enough Satisfaction points, they can buy Mermadic kelp for 500 points.

One thing you should know about becoming Merfolk with Mermadic kelp. Your Sim must go in the ocean before the moodlet that says something like, I feel funny and have an urge to go in the ocean disappears. If they don't go in the ocean, they won't turn into Merfolk. Hope this helps! :)

EDIT: BTW, there's a lot of things Merfolk can do, probably more than I myself know since I just created a Mermaid myself and haven't explored everything yet. I'm sure there's lots of videos about TS4 Mermaids though on YT and doing a search in the forum would probably yield a lot of information too. :)

Perfect, thanks for your answers. Next question, where can I find the conch?

Ah-ha! Just found one :)
If I have one in my family, do they still have to be outed?

I just added mer-people to a club and all except one swims in mermaid form. Conch shells can be found around the lagoon on the different beach areas; one area is the beach in front of the two unusable beach houses and if you also follow the trail “your” far left of the two beach houses you will find shells. There also shells on the beach across the lagoon from the sand bar, and if you follow that beach all the way around to where it flows into the ocean shells should be on that beach to your left. There is also two or three shell areas in Lani St Taz; one area is on a distant secluded island, the other is near one of the small lot houses.

Once a mermaid is added to the family, they shouldn't hide it from the household.

I finally have outed two of my mer-people, and they went for a swim together, and they have tails. Great fun!
Thanks all for your help. Much appreciated.
I was under the impression that they'd all be basking among the rocks from the moment I installed the game :D