Answer

Regarding Kiddush, I do not see any obstacle. See Shulchan Arukh, Orach Chayim 271:1-2. And the reservations mentioned in the Mishnah Berurah and the halakhic decisors there, based on the Talmudic statement that “a curse comes upon him,” do not seem substantive in my opinion.
As for Havdalah, one must consider whether this is a time-bound positive commandment, from which women are exempt, and therefore they cannot fulfill the obligation for others, or not, since it may be like the other prohibitions and commandments of the Sabbath, for which women are obligated. See the dispute about this in Shulchan Arukh, Orach Chayim 296:8, and in the Rema there. However, the halakhic decisors wrote that a man who already recited Havdalah in prayer is then obligated only rabbinically, and in that case a woman can fulfill the obligation for him.