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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The scholars differed in opinion about the number of the Jews who died in the battle of Banu Quraythah. The least number that was reported in this regard is that they were 400; this is proven by an authentic narration reported by At-Tirmithi and An-Nasaa'i . The highest number that was reported is 900, and this is reported as you mentioned by Ibn Is-Haaq .
You should know that the Jews of Banu Quraythah deserved this as they betrayed the covenant. For more benefit, please refer to Fatwa 99502.
The scholars also differed in opinion about the issue of Rayhaanah. Some of them stated that she embraced Islam and the Prophet married her after he freed her because she was a slave girl. However, some other scholars stated that she remained as a slave of the Prophet . For more benefit, please refer to Fatwa 90599.
As regards the narration on the woman from the Jews of Banu Quraythah who was killed, it is a Saheeh narration. The interpreters of this narration stated that the reason she was killed is that she insulted the Prophet . This is the evidence given by many scholars that whoever insults the Prophet should be killed.
You should know that Muhammad ibn Is-Haaq is a great scholar, and he is the author of the book entitled Al-Maghaazi (The Conquests), which is a reference book in biography and history.
As for what Imaam Maalik said about Ibn Is-Haaq, then this statement should not be considered as stated by the scholars because these two scholars lived at the same time and they might have had some arguments between them.
In addition to this, what Ibn Is-Haaq stated and which you mentioned in the question was also reported by other scholars .
With regard to the wisdom of the 'Aqeeqah being two sheep for a male born baby and one sheep for a female born baby, then the scholars stated that this wisdom could show the virtue of the male over the female. This is the legislation of Allaah; He should not be questioned about what He does.
Finally, it should be noted that it is acceptable to slaughter only one sheep for the 'Aqeeqah of a male infant as the Prophet slaughtered one sheep for the 'Aqeeqah of Al-Hasan and one sheep for Al-Husayn .
Allaah Knows best.