They don't have anyone to look after them? And they're eight? What comes to mind is they would all probably wear dresses and mismatching clothes. They would probably wear loose, thin clothes to feel less restrained and they would wear clothes about twice or three times their size. Since they've goner around naked for the past eight years, they probably would wear any kinds of clothes that seem most comfortable to them, nothing too tight or constricting. I'd love to carry on this conversation, but it's past midnight and I need my sleep, so don't feel too bad if I don't reply after this. Good luck with your characters!
As a woman used to wearing short-shorts and tank tops, I'm imagining how I'd react if I were thrust into a society where I was forced to wear a thick full-length burka with a face veil all the time...I see your character's situation as being the equivalant. And how did they not drown in the sea? Are they former mermaids or some other kind of superhuman race? Their social skills would be really, really undeveloped. Like maybe to the point of seeming mentally challenged, even if they aren't, because they probably haven't developed the skills most kids learn. Even kids who don't go to school still interact with other kids and experience situations that test their problem-solving abilities, so your MCs would lack here. On the other hand, they'd excell in wilderness survivial skills that their peers may lack.
Just a thought though as they had been living in the sea with it surrounding their skin all the time it maybe the reverse going from wearing a Burkha to short-shorts and tank tops. Personally I think you should write a scene and decide how things felt in the sea.
His clothes would itch or tickle or both. He might soak them in water just to get the closest feeling to what he is used to. Not necessarily a mistake. He could form his own fashion heedless of social conducts - he could wear pants on his head. He might wear only a shirt or nothing but shirt and shoes because an underwear feels too tight on his male parts... Is your story humorous? Is it led by humor?
Like there's nothing wrong with it, it's just not accepted there. Let's say you listen to metal, but you're visiting your ultra-religious/proper relatives who don't want heavy metal played in their house. So you refrain from playing it out of courtesy and because you know it's not accepted/desired, and you can tell the difference of when to play your music and when it isn't, but you don't feel there's anything wrong with your music. That's how it'd be with their nakedness.
It wouldn't probably be weird on its own, but they'd wonder why they had to do it, since that would never have been needed before. Similarly, do they even have sweat glands? The only thing that makes humans smell is that our sweat grows bacteria in our clothing, but not on skin so much. Also, have they ever been on the surface of water, or have they been deep under water without much daylight, or without contact with the air? Do they know humans exist before going on land? Would they have trouble adapting to above-water noises? There are less reverberations and more sharp noises above water. If you don't want to go into that, you could always just say it's a product of being half-human.
Does this affect things? Merfolk are born as legged, air breathers and raised on island nurseries. Around age six they form a coccon and emerge as tailed water breathers. The MC's went through this but retained legs, due to their human fathers.
Well they spend their babyhood in half flooded caves, they can breath, their parents can swim around.
Well the caves are open to the outside so there is light. So not as bad as it sounds. Also half flooded probably sounds rather nice to a mermaid.
but you are suggested they go from 'human' to 'merfolk' almost. For me it seems like evolution backwards.
I guess it feels like they are going back into the sea, which humans are supposed to have evolved out of. From an evolution point of view it seems odd. Also if they breathe air, have legs etc What stops them getting chest infections and trenchfoot in the caves ?
But reverse from everything else on earth ? When they come out of the water and the caves are they in a hot climate or a cold one ?
no but I am curious why they don't burn ? Like I am curious why they don't get trenchfoot in a wet cave ? What if they come out on a nudist beach ?