nevlastní bratr znamená v angličtina

half brother [half brothers]▼(male half-sibling)
noun
[UK: hɑːf ˈbrʌð.ə(r)] [US: ˈhæf ˈbrʌð.r̩]

stepbrother [stepbrothers]▼(son of one's stepfather or stepmother)
noun
[UK: ˈstep ˌbrʌð.ə(r)] [US: ˈstep ˌbrʌð.r̩]