Ruling on discovering one's wife is a sister by breastfeeding

Q 2: A man married a woman, but after they had a son and a daughter, it was confirmed that she was his milk-sister. What should he do? Will he and his children - upon their attaining the age of discretion - be held accountable for this sin? Is it permissible for the children to marry or do they have to refrain from marrying until they die? (Part No. 21; Page No. 71

A: If a man marries a woman without knowing about the prohibitive impediment against the marriage and only discovers after concluding the marriage contract that his wife is his milk-sister - i.e., that the breastfeeding occurred five times during the first two years of her life - it is obligatory for the contract to be dissolved and for him to leave her. This is so regardless of whether they consummated marriage or not, or had children with her or not. As to his sexual relations with her before knowing that she is his milk-sister, this is not regarded as Zina (sexual intercourse outside marriage), instead it is considered as a doubtful marriage, and he is free from blame as he thought that she was his lawful wife. As to the children, they are attributed to him and entitled to all the rights of children born within a valid marriage and therefore have the right to inheritance and Nafaqah (obligatory financial support). Their birth to these parents in this way does not prevent them from getting married; they may marry in the same way as any other Muslim. However, it is necessary that, before any Muslim concludes a marriage contract, they must make sure that there are no prohibitive impediments such as connection by marriage, breastfeeding, etc., then they can proceed to marriage when they are quite certain that there is nothing about the future spouse that forbids marriage.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.