Do they allow mono fins and mermaid tails?

Yes

Here's a more recent answer just in case you don't trust the "two years ago" answers. I have a mermaid tail from finfolks productions and I wear it all the time. They don't allow you to wear it in the deep end though.

I've seen families with both swimming but it's possible that policy was changed or wasn't enforced that day. You could call and double check

Yes. I have seen several wearing mermaid tail

Yes they do

Yes, my kids have worn them there several times.

I've seen others wear them