Complex sentence: Men from the "Brothers" who had been in the vicinity of Otago Harbour proceeded south late in 1810, seeking a passing ship to take them back to Sydney, but four of their number were surprised and killed, apparently just because they were Europeans.
Split into simpler sentences: Men from the "Brothers" who had been in the vicinity of Otago Harbour proceeded south late in 1810. They were seeking a passing ship to take them back to Sydney, but four of them were surprised and killed, supposedly just because they were Europeans.