Is it permissible for the groom's father and the bride's maternal uncle to be witnesses to the marriage contract, or must the two witnesses be non-relatives?

Everyone who attends the marriage contract is considered a witness to it, and it is not a condition to be designated by signing the contract. The maternal uncle of the woman and the father of the husband are permitted to be witnesses. What is prohibited is the testimony of the woman's guardian (wali). It is a condition to have two just witnesses other than the guardian. The term "guardian" (wali) here does not refer to the person who officiated the contract, but rather the one who possesses guardianship over the marriage.