I’ve just met the merfolk and some don’t even have the option to be talked to. All of them have locks on the hearts that indicate relationship status. I’ve started working on the |deep sea| and I don’t know if these things are locked due to the story or if it’s a bug.
#Merfolk Friendships
cinder cove
indigo kestrel
from what I've searched, you need to complete enough of the healing the ocean questline. I'm on 'Heal the Coral Tree' right now and don't have relationship options yet
thorn island
As Keenan said you need to work on the main story. After a certain point you’ll be able to befriend them
rain sorrel
You need to finish ||"One of Us"|| quest and then you will be able to talk to merfolk npc and gain relationship