Before I start this I just have to say: you asked for it
So since mermaids are mainly human, I would assume that they are mammals. That means that a merman would have to get a mermaid pregnant just like humans. But they do have tails which cover up where the human genitals would be. We don't even know how do they go to the bathroom? Well maybe they're genitals are end of there tails! For a merman to get a mermaid pregnant, what if all they had to do was essentially put one tail in the other. News flash– 🧜♂️the little flap at the ends of their tails are mermaid-protection. And in case the water gets to the right temperature, they give the protection to everyone, even children. The mermaid gets pregnant just like any human would, but out of their tails. Then after *insert time here* the child is ready to come out of the mermaid's tail. That would definitely be very difficult for the mother because the tails get smaller as they reach the bottom. But then why don't the mother's tails have marks? They get new scales. The mother must have lots of time after the birth to recover, which is probably why Ariel had so many sisters, because their mom loved having all that time to just lay there while her tail gets back into normal form. Then when the mermaid has had enough time to fully recover she must do it all over again or actually take care of her family.
