I am a revert but with Muslim family in other countries (i.e. my paternal uncles). My father is deceased which is why my brother and I were raised no Muslim. My brother is also a revert now but is in jail. I live with my mom and she is unmarried and is Christian. Her father (a nonmuslim) is the only mahram I have in this country besides my brother who is in jail. In this situation, who is my wali? Would it be the imam at the masjid I attend, or would it be one of my paternal uncles? Or is it still my brother?.
We praise Allaah for having guided you to Islam, and we ask Him to increase you in faith, knowledge, steadfastness and guidance.
The woman’s wali is her father, then his father (i.e., her grandfather), then her son, then his son (i.e., her grandson) [this applies if she has sons], then her full brother, then her half-brother through her father only, then the sons of her full brother, then the sons of her half-brother through her father, then her paternal uncles, then their sons, then the father’s paternal uncles, then the ruler. Al-Mughni (9/355).
The grandfather who has the right of guardianship is the grandfather on the father’s side. The mother’s father cannot be a wali. Based on this, your wali is your Muslim brother; the fact that he is in jail does not prevent him from being a wali. It is possible to contact him and visit him, and at that time he can delegate someone to do the marriage contract for you on his behalf. If that is not possible, then your wali is your paternal uncle, and it does not matter that he is in another country. He can delegate someone to do the marriage contract for you, or the marriage contract can be done by modern means such as the telephone and internet.
We ask Allaah to bless you with a righteous husband and righteous offspring.
And Allaah knows best.