In many legal systems, including those governed by Islamic law, witnesses in cases like triple talaq are expected to be impartial and credible. Relatives, especially those closely related to either party, might be considered biased or not accepted as valid witnesses from the wife's side due to potential conflicts of interest.
The rationale behind this is to ensure fairness, impartiality, and the credibility of witnesses in legal proceedings. Courts generally seek testimony from individuals who can provide unbiased and truthful accounts of events without any personal interest or familial ties that might compromise their objectivity.
However, specific rules regarding who can serve as a witness can vary based on cultural interpretations, regional laws, or individual circumstances. Consulting legal experts well-versed in Islamic law or family law would offer precise guidance on the admissibility of certain witnesses and the legal principles governing such cases.