After review, if Jewish fathers are not allowed to marry their non-Jewish daughters after they convert, then that's not permitted either, since it's a rabbinical commandment for this generation. If we can get rabbis to change it, and believe me I will be the first to sign onto that, then it could be, but it's not allowed today, and you make two sins from the Torah to do that because of the rabbinical judgment.
different cases. First off the legal fact that a Jewish father who fathered a non-Jewish daughter (through a non-Jewish mother) is forbidden by Rabbinic law. It was always forbidden, and its forbidden and not subject to change, ever.
The whole point of stating that was only to teach a Jewish man not to have children with a non-Jewish mother because technically the offspring are not "his children in the eyes of G-D". That doesn't and never did all him to then be with them since they aren't his children. Its more of a moral lesson.
- Their is no and was no real Rabbinic enactment with the power to prevent a man from marrying more than 1 wife. Some claim Rabbeinu Gershom but only up to 1,000 years. Guess what, it passed.
Thus your claim that the children would be "mamzerim" is false.
Soo the 2 sins, what would they exactly be?