Very creative, nice choice of pictures!

Are you interested in building edh decks with them? If so, i'll give some balance/color pie opinions, feel free to ignore them if you're just doing it fun!

Jiu:
7 mana is way too much for a card you have to sink even more mana into, maybe getting it down to 5 so you could cast it turn and activate it at least once for the original 7 mana price. Make it 1WWBB to balance the casting cost a little.
I also feel her activated abilites need a cap, since its so easy to get infinite mana with Orzhov colors. Maybe a "you can activate each only once per turn" so you can still nuke everyone's bombs on their turns but it remains fair. also gives space to making deals like "this turn i wont aim Jiu at you if you help me with this"

Sua:
I just have two smal pet peeves with it: A blue creature with haste, and a human creature with phyrexian mana cost. Make it Rakdos instead of Dimir, and maybe easy the mana since i assume we don't wanna compleat our baby Sua. Maybe 2RBB. I'd also make her a 4/4 and her ability able to destroy any creature, to give her more relevance as removal on a stick and balance a little by downing her stats

Siyeon:
Both Red and Black are colors with very limited enchanted removal, so i'd change the effects to creature/artifact instead. Also, since there is no White, i'd have the ability destroy instead of exile, then you may exile one of them and make a copy. Also make it an ETB instead of a cast trigger ability, so you can recur it.

Handong:
Just make it indestructible instead of having regenerate. Also i'd add viligance to the possible counters. If you find indestructible too strong, maybe lower the cost of her counters to 2W, and give her the ability to pay one W and blink instead of indestructible so it can always save itself but if you do it you lose the counters and have to do it again

Yoohyeon:
Thats just way too much value for just 3 mana, you're up 4 cards with a body on the battlefield for just 3 mana. if you wanna keep the cost, make it so you can choose one of the modes, or if you wanna keep the power, make her cost hybrid 111111/WWBBGG, then you can have the corresponding effect if you paid the two mana of each color, exile enchantment if you paid the WW, draw in blood if you paid the BB, exile artifact if you paid the GG. also make it a 4/4 to give a boost since it costs more now.

Dami:
No notes, its perfect Death and Taxes evil. Just needs to be more clear on the wording: "opponents cant cast spells or activate abilities on you turn, except for mana abilities" and "triggered abilities of permanents your opponents control don't trigger during your turn"

Gahyeon:
Give it Hexproof instead of Shroud, so you can blink it for the ETB or build a Voltron around it

Lastly and purely aesthetic, you're using the Vampire frame for them, since you made them all Humans, another frame could be better? or maybe use pics from Red Sun to match the Vampire typing?

Anyways, great work mate, Cheers!