What if a Kohen married a woman who he was not fit to marry such as a woman that had slept with a non Jewish man prior to their marriage and they had son which would make the son a chalal. My main question is this happened in the early 1980s in Iran and their family was not religious and they were poor and they did not know fully Torah law. If a Kohen does not know full Torah law and marries a woman not fit for him because simply they are not religous and do not know the law and had a wedding likely without a Rabbi to instruct them does that still make the son a Chalal? Are there questions of whether the son may or may not be a chalal because it was not the sons fault that the parents were not religous and did not know fully the Jewish law back then.

ב"ה Shalom, The circumstances are totally understood, however if a forbidden marriage with a Cohen took place and a Chalal was born it cannot be undone, regardless of the circumstances. However, with all these types of questions, you need to approach a Rabbinical judge who is fully fluent with issues of marriage with the exact details as every case can ruled on differently depending on very slight differences. I may add that it would even be better to find a Rabbi who is either originally from Iran or is fully knowledgeable of the backgrounds of different communities in Iran, for this knowledge may also have ramifications on each case. All the best