Ain't no way your that dumb to not know there siblings they look the exact same

But the one law of BL, no matter is it manga, manhwa or manhua, is that there is no siblings, unless those are enemies as drama plot devices.

The only exception of the rule is uke has much younger sibling or siblings he needs to care for - so that is the motivation for uke staying with seme.

That is literally not true, countless BL leads have perfectly normal siblings with a reasonably small age gap. I'm crine who told you this "law" existed ╥﹏╥