Is it permissible for my younger brother to be my guardian (walī) in the marriage contract, knowing that my mother was pregnant with me when she married my father? And does this entail not mentioning my name as "So-and-so, daughter of my father's family name"?

A woman who committed adultery is not to be attributed to the man who committed adultery with her, nor to her mother's husband. Rather, she is attributed to her mother, so it is said: "So-and-so, daughter of So-and-so." Otherwise, the guardian (Wali al-Amr) should choose a common name for her that does not refer to a specific person. The daughter bears no sin for her parents' actions, and her patience in enduring harm will be rewarded.