As an older sister, I am called *Ate*. Meaning older sister. Younger sister is *Nakababatang kapatid na babae* when more formal, or just *Kapatid na babae* when not being formal. Older brother of *Kuya*. Younger brother is *Nakababatang kapatid na lalaki* for more formal or just *Kapatid na lalaki*
Or just say: kapatid. And that kuya and ate are very commonly used, not just for siblings, but also as respectful terms for slightly older people. These people include family friends or friends who are older than you.