Does Tsuyu Have a Sister?

Satsuki Asui (蛙吹さつき, Asui Satsuki^?) is Tsuyu Asui's younger sister.

Does Tsuyu have any siblings?

The summary reintroduces the Asui family as Tsuyu is reunited with her two younger siblings, Samidare and Satsuki.

Does Tsuyu have an older sister?

She has a brother and a sister and they are both younger than her (the sister is around the same age as Eri and Kota). They were first shown in the little extra chapter on Tsuyu, along with their parents. I don't know if the second light novel tells more of them, or of more siblings - never heard of an older sister.