|KYOU / KEI||
as in "KYOU (今日) my older brother acted OK. Tomorrow he'll be a bully again. "
My older brother is eating so much, he is basically a mouth on legs.
|( お ) にい ( さん )||
older brother (used about ANYONE's older brother, or even ANY guy that strikes you as being of an 'older brother' age, almost like you could substitute niisan for 'dude')
older brother (used about YOUR own personal brother)
siblings (not just brothers)