Praise be to Allah.
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.