A reference to a brother or sister in a will generally includes a half-brother or half-sister. This however, is a question of interpreting the will.
Where there is no will, the Administration and Probate Act 1919 (SA) draws no distinction between full and half-blood [s 72]. So a half-brother or half-sister would qualify, in the statutory order of distribution, for her or his half-brother or half-sister's estate.