These two Fataawa about illegitimate children are not contradictory
2-11-2010 | IslamWeb
Question:
May Allah bless u,i often take fatwa from this site and also read previous fatwas to increase my knowledge.thanks for guiding muslims to the right path.But two differebt fatwas on the same topic made me confused.I want to ask and be thankful if u give me answer, 1,In fatwa no. 83680 and 122443 u were asked the same question that is nikah of a man with a woman pragnant from zina with the same man ,these fatwas differ abiut the attribution af child to the biological father.If the nikah is haram after the pragnancy is confirmed then why one should count the months for attribution of child to him as he already know the woman is pragnant before nikah from zina. 2,similarly i am confused to read two different fatwas by u in fatwa no.91451 and 86518 where in one fatwa u say that zina does not make the woman s mother or daughter haram for zani ,and only marriage make haram.but in other fatwa u say zina makes haram the mother and daughter of zania for the man who comit zina with her
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
There is no contradiction between the two first Fataawa; the second Fatwa only clarifies some details that were not mentioned in the first Fatwa, but the meaning is the same.
If the mother of the child who is mentioned in the second Fatwa was pregnant with him for five months before marrying that man, then she would give birth to him less than six months after she married him, and so the child could not be traced back to him.
As regards calculating the period of pregnancy, then in order to know the possibility of this child being from that man, then the jurists 
stated that if a man has a wife and she gave birth to a child in a period during which this child could be considered from him (i.e. six months after being married to him), then the child is traced back to him and he becomes his father, so the ruling of inheriting each other and other rulings that apply to birth apply to them; this is whether or not the child resembles him. That is because the Sharee’ah is keen on tracing back the children to their possible fathers, and the period of the possibility of the child being from his father is six months from the time they (the husband and the wife) got married.
Additionally, committing Zina (fornication or adultery) with a woman whether by the one who married her later or by someone else does not necessarily mean that a pregnancy would have occurred so that it can be authoritatively asserted that this pregnancy - to which the woman gave birth after she became a wife and in a period during which the pregnancy could have been traced back to the person who conducted the marriage contract with her - is from Zina.
With regard to the two last Fataawa, there is no contradiction between them as well, as one of the Fataawa referred to the other Fatwa where it is mentioned that there is difference of opinion among the jurists in this regard in order to clarify that this issue is not something agreed upon among the scholars, and this last Fatwa did not consider any of the two opinions to be the preponderant opinion.
Allaah Knows best.