Responses

The kids who said "are you really tsukasa? why are you crossdressing?" were her friends not her brother (I suggest rereading the chapter if you are confused ^.^) the guy in question who said this line looks very similar to one of her brothers but it's not the same person. All of her brothers know that she's a girl. In fact, if you examine the drawing you can see that she is still hugging her brothers when the friends come up and ask that question.

Nah all her brothers know not just the big one
spoiler ? lol idk
http://www.mangago.zone/read-manga/tokyo_crazy_paradise/an/tokyo-crazy-paradise-chapter-16.html/21/
Do the siblings not know shes a she???????? I mean their parents didnt hide it from them as well did they? because it doesnt seem like the younger brother knows?