The first part wasn't as complicated to Cora. Her people were granted one day a year to walk among the land dwellers. And enchanted bracelets, necklaces existed in her world that allowed people to change forms. A spell from a witch, a puff of green smoke, and other tricks could change people to mers too.
"The spell doesn't matter as long as you and she are happy with the results." She said; she could offer to share her bracelet, let them walk with land legs when she wasn't using it. It was hard to share though, hard to trust anyone to return her bracelet. "Your portals sound even more unpredictable than mine."
"Cristiano's world sounds the most like mine. We had a nation once, under King Poseidon. But then the wars with the pirates started, the sea witch became powerful and we were separated out. We all come together once a year for a great ball. A magical night." She smiled at the memory. Before she found the bracelet, that had been the only time that she could experience both worlds. "What's the future like?" She asked. Twenty years without a curse sounded good.