1)
What is the meaning of "u'Farsu ha'Simlah"?
1.
Rashi (from the Sifri): It means that they clarify the matter like a new garment. 1
2)
Why does the Torah write "Velakchu ... es ha'Ish" and not "Velakchu oso"?
1.
Sifri: To preclude a Katan. 1
1
Torah Temimah: It is not clear however, as to why this D'rashah is necessary. See Torah Temmah, note 143 and ha'Torah ve'ha'Mitzvah, Siman, 93.
3)
Since it is the father who speaks ("es Biti Nasati ... "), why does the mother also spread out the garment?
1.
Ramban: Because it was generally the women who dealt with the cloth and who were more expert in matters concerning the blood.