Is it permissible for a maternal half-brother to be the guardian (wali) in the marriage contract of his maternal half-sister, knowing that her father is deceased and she has no other guardian than him?

A uterine brother (maternal half-brother) cannot be a guardian (wali) for his sister unless he is also her paternal cousin (ibn ‘amm) and no closer guardian is available, or if all her legal guardians, including the judge, are absent. A marriage conducted without a guardian is invalid according to the majority of scholars, but it is considered valid by Imam Abu Hanifa if a Sharia (definition) judge rules it to be so.