So, all the children that swk has are 100% yaoguai monkeys, or are some of them human? I think King Paramiya and Yuebei Xing have human appearance? I mean the ancient writings, not books or adaptation of JTTW.
It’s hard to say as we don’t get a lot of information about them.
Paramita is easier to at least know what he could look like (however please keep in mind that this is a dream and that Paramita technically wouldn't have to follow any set rules due to being in a fantasy) as we know that his mother is Princess Iron Fan. He was not conceived in the traditional sense however as he was born when Wukong accidentally got Princess Iron Fan preggers when he jumped in her tummy. Funny enough he did this to like four other demons as well so... perhaps we know where Paramita's four unnamed brothers came from. Joking of course, it is said that Paramita's four other brothers are also Princess Iron Fans BUT THAT WOULD HAVE BEEN FUNNY.
The only description I can find in the book about Paramits is that he is "dashing" and this might cause he takes more after Princess Iron Fan. Sadly, looking like a monkey-yao was not considered "dashing" and therefore I think decreases his chances of being as such. Paramita would be half monkey yao and half Rākṣasī if he was real. There is few other pure yao children in mythos, the only one we really can compare him to is Red Boy (who doesn't exist in this fantasy dream) as he has a very human-looking appearance as well. I talked a bit about this, but it could be that since Wukong and Iron Fan are already very cultivated that their children would take on a human-like appearance to show this. In any case, Paramita wouldn't have any reason to look human since neither his parents are human, but still, he has powerful parents who have cultivated to a human form he would be able to have a human form as well.
Of course, there is a part in the Supplement JTTW where Wukong meets another version of himself but as an old man. Wukong is still a monkey but he sees another version of himself as well but as an old man that is his "true spirit" in Chapter 10. This is strange cause Wukong in his dream was he was called "only having a monkey face" but he wasn't Sun Wukong because he wasn't a Monkey Yaoguai. This could be saying that Wukong in his dream transcend his own monkey body and form and rather moving into a full human form. This would increase the chances of King Paramita's hypothetic form being seen as all-human if this was the case as well.
On the left is the White Ape Perfected Man that I think Wukong's "true spirit" would look like in Supplement. On the right is King Paramita from a modern Comic Strip published in 2021 as there is little to no other modern interpretations of King Paramita.
Yuebei Xing and her brother are a tad different and harder to pinpoint due to their mother being unknown. Certainly, they are half-monkey-yaoguai but as for mothers, it could range from another monkey yao to a mortal to an immortal to even Wukong using the baby river himself. Hard to say but there are possibilities.
If Yuebei Xing's mother was human than the chances of her and her siblings looking human increase greatly. However, if they are a yao then they COULD look human with some cultivation but that doesn't mean they would be born looking human guarantee. This is also a story that would be based more on the Xiyouji Zaju play Wukong where he kidnaps his human-wife in the introduction and doesn't reach Buddhahood by the end of the play so it would be within reason to believe that Wukong got another human-leaning wife whether that be mortal or immortal.
But unlike Paramita, Yuebei Xing DOES have a description!
"Monkey King had a daughter named Yuebei Xing. She had a crooked head with large eyes and a broad mouth, a wide waist, thick hands, and long feet with thunderous footsteps. Every time, she would utterly defeat her enemies. Yuebei Xing stepped forth, "I'm going too." "You were so ugly," the little Suns roared with laughter, "You will become a laughingstock in front of Huaguang.""
She is described as more outlandish in form and even called ugly, however, this could be that she simply takes more after her father's face as he was called ugly as well.... or maybe she is only ugly by monkey standards, it is hard to say. Despite this description, however, it does not say that she looks like a monkey or a human as while a detailed list of what she has, doesn't lean towards human or monkey either way.
I'm taking from @journeytothewestresearch page about his articles for Yuebei Xing but she is noted to have two forms from Secret Practice of the Primordial Lord Yuebei 元皇月孛祕法. So this is not from the same author as JTTS but can still provide some idea of what her past interpretations could have looked like.
"In the form of a celestial human, their hair is let down over their naked body. Their mass of black hair covers the navel. Red sandals. Their left hand holds the head of a drought demon. Their right hand holds a blade. They ride a jade dragon. In their modified form, [they display] a blue face with long fangs, a crimson garment and blade, while driving a bear." (Kotyk, 2017, p. 62).
It could be that in JTTS was learning more to her modified form as she is given more extravagant details to her description.
The left image is of Yuebei Xing in her celestial form with her sword in hand. On the right is where she is drawn as a man but still holding her sword and severed head.
However, these are descriptions based on Yuebei Xing outside of JTTS and therefore would not be considered to have any monkey relations to her. If that is the case then that could be as to why the author of JTTS didn't describe her celestial form or her modified form as he was creating a new original look for her NOW that she is half-monkey. It wouldn't be fair to say that she is one or the either considering that now her origins have not only changed but also are unknown who or what her other parent is either.
So overall I can't say that they can be 100% monkeys as King Paramita is half rākṣasī and Yuebei Xing (and possibly her brothers) are most likely not from a monkey-yao mother. But while Paramita wouldn't look monkey himself there could be hope for Yuebei Xing and her brothers since their origin has not only changed from her previous depictions but also that her mother is left to interpretations. So while the chances of her being 100% are low they are not impossible at the very least.
Take it as you will!