兄弟【きょうだい】
siblings, brothers and sisters, brothers, siblings-in-law, brothers-in-law, sisters-in-law, mate, friend
実兄【じっけい】
biological older brother
兄さん【にいさん】
older brother, elder brother, brother (as older-brother figure in friendly and or work relationship), young man, buddy, fella, laddie
義兄【ぎけい】
brother-in-law (spouse's older brother or older sister's husband), older stepbrother