Do you know what Oni-chan and One-chan mean? 

Onii-chan and Onee-chan is nothing more than an informal way of talking big brother and big sister. 

Onii [お兄] literally means older brother and Onee [お姉] means older sister. Chan is an honorific of childish treatment, informs and intimate, as if it were a diminutive (little sister).

The most formal and common is to use the suffix san, that's why we also hear the words a lot onii-san for older brother and onee-san for older sister. 

There are other ways to say brother in Japanese such as:  Kyoudai Shimai ani Anne  otouto imouto futago I gave Gimai Each shape is specific to something like age and sex.