MARKS FOR POSSIBLE SPOILERS
Yuma's the youngers of Mirai and Kazuma Tsukumo
He seemed to have a good relationship with both his parents and it's implied he was a little spoiled, given Akari, his older sister's, reaction to him getting to go places with Kazuma
With his mother, it seems like he has a typical relationship that any boy has with his mom. Loving, nurturing...beyond that not much is shown with either of them.
With his father? Well, Yuma looks up to Kazuma a lot and obviously tries to emulate him as often as he can. He remembers almost everything his dad told him before he left and takes all of it to heart
I feel like Yuma would do anything to keep his father's memory alive. Not only that, but he would do anything to be closer to him, given that neither of them are around anymore, given that they are "missing"
I think that he'd take up an interest in his father's work, his travelling and places he went to. Ruins, Ancient Civilizations, because it's something that keeps him close to both his parents
As for Akari, their relationship seems...odd
It seems like the normal brother-sister relationship in the fact that they argue, but I feel like Akari tries to hard to be a parent and that's why Yuma is so stubborn with her
I feel like they would do anything for each other, if something were to happen to either of them, but at the same time, I think that their age difference and the fact that Akari is still growing up too doesn't
help them. It's like a similar situation to Lilo and Nani in lilo and stitch
I think he's a pretty obedient grandson, she makes the comment that he is
He probably helps her out when he can, and I love imagining them sitting at the dinner table talking about their days
and them just laughing over the same jokes and things
III, I mean, his family dynamic is shown pretty well, not as well as I would like but
I feel like III has a less awkward relationship with IV then he does with V
mostly because they have been together for a long time
and he doesn't worry about V as much as he does IV
As for his father, III has this overwhelming need to take care of him.
He wants to make sure his entire family is alright, but I'm sure that with Byron being the way he is, he is a little crazy about taking care of him.
AS FOR MOM, I headcanon she passed away when III was born, but he looks exactly like her
HARUTO'S NEXT LET TALK ABOUT SOME TENJOUS
Haruto's main relationship is obviously Kaito
He admires Kaito, loves him dearly and wants nothing more then to see his brother happy.
Haruto, though, also wants Kaito to let up a little bit, because he's doing better and wants a chance to experience a lot of things, not just stay in the tower all the time
AND BECAUSE WOW NII-SAN HE CAN WALK BY HIMSELF
but he views Kaito as a parent figure as well as his brother, so he respects him and probably tells Kaito if he's doing something out of habit, and forget to tell their dad
Haruto's relationship is probably not as awkward as Kaito's is when it comes to their dad
he's probably the one constantly trying to get them to at least talk and spend SOME time with each other
but he still views his dad as someone who caused a lot of trouble for him, even if he understands it was what his father viewed as the only method
As for mom, I don't think Haruto knew his mother, I believe she also passed too, given she was sick and frail like haruto
But his eyes and hair come from her
which is likely why faker wanted to save him so badly
EITHER WAY, Kaito is the most important thing in Haruto's life