I don’t think you are going to find an online source. You are going to have to crack open some books.
Intent is the key. As long as there is some hope that intercourse may occur the couple may proceed. If there is a missing male organ well then that would be hopeless. I think the couple would know if there was hope or not.
Since marriage cannot occur when there is absolute assurance of impotency I think it’s fair to apply canon law and take the step to sexual activity within marriage if there is absolute evidence of impotency.See Canon Law.
Canon 1084.1 of the Code of Canon Law of the Catholic Church states that “antecedent and perpetual impotence to have sexual intercourse, whether on the part of the man or on that of the woman, whether absolute or relative, by its very nature invalidates marriage.”
However, Canon 1084.2 adds that “if the impediment of impotence is doubtful, whether the doubt be one of law or one of fact, the marriage is not to be prevented nor, while the doubt persists, is it to be declared null.”
Course I’m not a Canon Law expert and only play one online sometimes.