Brother-in-law: the spouse's older brother or the husband of one's older sister (a non-blood older brother by marriage).
私の義兄は来月結婚記念日を祝うそうだ。
My brother-in-law is apparently celebrating his wedding anniversary next month.
義兄（ぎけい）は忙しくてあまり会えない。
My brother-in-law (gikei) is busy so I rarely see him.
彼は義兄に当たるが、実の兄のように親しい。
He is my brother-in-law, but we're as close as real brothers.
Older stepbrother: a non-blood-related older brother (e.g., from remarriage or adoption).
両親の再婚で義兄ができたが、すぐに打ち解けた。
When my parents remarried I gained a stepbrother, but we got along quickly.
義兄とは子どもの頃から同じ家で育った。
I grew up in the same house with my stepbrother since childhood.