Miriam spoke to the men , saying that they should sing first. The men had already sung their praises and now the women were about to begin. The angels complained to Hashem that they had already waited for the men to sing first, but they did not want to wait until after the women sing. Miriam responded that the angels should sing before the women sing. The women had greater trust in Hashem than the men had, as indicated by their bringing along musical instruments, and were more courageous than the men.
Courage is a manly characteristic, so the verse expresses the women's actions in the male form.
As mentioned earlier, the women chastised the men for not bringing along musical instruments. However the gemara Brochos 17a and Sotoh 21a says that women have the merit of Torah study by virtue of facilitating the Torah study of their husbands and children. The proof that a facilitator has equal merit as the one who actually carries out the act is seen from the fact that the horses of Paroh's army also drown along with the riders. The horses had done nothing wrong and were only punished as facilitators. This is why the drowning of the horses along with their riders is specifically mentioned.