I feel like a lot of Kuai's clothes were just Bi-Han's hand-me-downs when Bi-Han got too big and they just threw it at Kuai since Kuai would be growing into it.

Not all of them were but I imagine a good portion of his clothes used to be Bi-Han's, especially before puberty.

I feel that will depend a lot on the timeline, socio-economic situation of Lin Kuei and how big the age gap is between brothers. 

For example, if in the new timeline Sub-Zero and Scorpion’s family is treated like a true Royals, then Kuai Liang as the second-in-line to the “throne”  is less likely to wear hand-down clothes, unless the cloth has traditional importance, like it happens with some items passed down from one generation to another. And that could be as much about Grandmaster and his wife’s wish to give only the best to their sons as much as a matter of prestige and upholding their social status. 

However, if despite the importance of the Grandmaster's role in leading the clan, Lin Kuei is in fact a large family unit first and foremost, with close personal bonds, I can see the clothes being handed down as a common practice - especially if the clan resources are limited. I mean, we hardly have any idea what Lin Kuei economy is based on in time of peace and there is something to say about Sub-Zero’s delight about spoils of war to which Scorpion did not disagree with the sole idea of spoils, only that they must first win the war.

Like, is Lin Kuei big enough to be a whole nation, with its industry, farming, cities and trade or do they live in isolated, self -sufficient society hidden from everyone else? Because to make clothes in the traditional way, you need specialized workers to hand -woven material in the first place, which takes time and a lot of hard work. The Lin Kuei brothers’ uniforms were most likely individually tailored which makes sense, as they are Grandmaster’s sons but also grown up and skilled men that worked hard to to be recognized as the warriors of the clan, but back in the time when they were children? It would be easier to store Bi-Han’s clothes until younger brothers grow up enough to wear them than to lose the limited material resources, as Kuai and presumably Tomas would outgrow the new clothes in a few months.

(Also, I’m speaking here from my family experiences, in which the clothes for babies and children were passed down between so many people over the course of years. So I’m here for Lin Kuei being the close-knit family that doesn’t mind hand down clothes between all the children as a way of supporting each other and providing the needed items. If Grandmaster’s family is a bigger unit, Bi-Han too could wear the hand down clothes before he grew up enough to get his own sets.)

Additionally, if Bi-Han and Kuai Liang (and Tomas) were close in age, the passing down of clothes feels natural and sensible. However if Bi-Han is older than 6-10 years or more, I don’t think his parents would store his baby/childhood clothes to collect dust and take up space in the closet, unless they planned to have another child at some point. 

As for the previous timelines, I think the situation is more complicated, because both Kuai Liang and Bi-Han were children forced into Lin Kuei. And a clan that kidnapped children to turn them into killers doesn’t sound like someone who would care what Bi-Han and Kuai Liang wished to wear or after whom they got their clothes.

The clan definitely provided its adepts with the necessary daily life items, but there is a question how much any of them actually owned anything? If adepts got the second-handed clothes and things were passed down between all children, both Kuai Liang and Bi-Han had a small chance to be given a choice what is given to them (unless the original timeline!father had a say in that regard). Could Bi-Han keep his old clothes, as in, have a place to store them for Kuai Liang when he was big enough to wear it? Could he even hand down his clothes in the first place, or would the clan treat it as mandatory equipment and "losing" anything were punished? I feel that in both original and alternative timelines none of the boys have a control over the clothes provided them by clan and if Lin Kuei practiced passing down clothes from one adept to another, as a cheaper and more pragmatic way in regard to fast growing up children, Kuai Liang may not necessary getting old Bi-Han’s clothes.

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