c.two
Haemophilia is X-linked and usually considered recessive - it is only manifested when in woman exists two X chromosomes carrying the haemophilia allele, or when in man exists one X chromosome, as in man there is only one X chromosome. If the mother has haemophilia, it means that she will always pass to her generation an X chromosome that has the allele for haemophilia. The father does not have haemophilia which means he does not have an X chromosome with the haemophilia allele, therefore, he will either pass an X chromosome without the haemophilia allele to a daughter or a Y chromosome to a son.
The two sons would have haemophilia because the only X chromosome they would get would be from their mother. The daughters, on the other hand, would not have haemophilia because they only get an X chromosome with the haemophilia allele - from their mother, while from their father they would get an X chromosome without the haemophilia allele.
Two of their children would have haemophilia.
