What sin did Cain’s wife commit to have equal punishment of her husband, being banished from God? Surely, God wouldn’t punish her just for being ‘married’ to Cain, would He? As there were no ‘priests’, etc to perform the marriage ceremony, how was this ritual performed, and by whom?
There’s no evidence that Cain’s wife was being punished in any way. Nor does the bible say that Cain was even married at the time of his banishment. Having a minister, rabbi, priest, etc. perform a marriage ceremony is a human tradition and is not required by God. In ancient times men and women were either married by mutual consent or because of parental arrangement.