I am about to marry a lady who has been divorced for many years. I spent shabat at her home with her and her kids.she made hamotzi on Shabbos.
1. Am I yotzei with her hamotzi?
2. Does the position change once we are married?
Provided that she intended that you should be yotzei with her blessing (if she was the one that made the blessing for everyone at the table, this intention can be assumed), and you intended to be yotzei, you are yotzei with her blessing. This arrangement can continue after you are married, but it is preferable that you should make the blessings (kiddush, hamotzi, havdalah, and so on) for the entire family, rather than her.
Sources: Although men and women are equally obligated in most blessings, it is proper that the man should recite them for the family, rather than his wife. See Sukkah 38a; Rambam, Laws of Blessings, 5:15.