the lupon is somewhat trying to be a court, it is highly irregular for them to place rules of evidence of their own, the lupon as govern by RA 7160 or the Local Government can arbitrate, mediate or settlement of dispute or conciliation. The question is more of a procedure as to the acceptance of the testimony of your sister in the dispute being heard by the lupon. You can call their attention that the rules of court are not applicable and only a court can determine the acceptability of the testimony of your sister unfortunately, it is only a lupon meeting and ANY testimony of the witnesses of both parties must be heard, and this must be reflected to the transcript of the meeting held. At the end, the lupon will only decide whether there is a possibility of settlement or not, and when one party fell aggrieved of the decision, he/she may ask for a certificate to file action in court. Now, it must be raised that the lupon should hear the testimony and not be a judge to determine the acceptability of it, so raise these to them, IS THE LUPON A COURT TO DETERMINE WHAT APPLICABLE RULES CAN BE APPLIED, ARE THEY ALLOWED TO DENY ANYONE TESTIMONY AND FOR WHAT BASIS, HOW CAN THEY DETERMINE THE PARTIES ACCOUNTABILITY IF THEY REFUSE TO TAKE THE TESTIMONY OF ANY WITNESSES. THE QUESTION OF ACCEPTABILITY OF THE TESTIMONY IS A COURT PROCEEDING, WHILE THE LUPON'S MEETING IS TO DETERMINE IF THEY CAN COME UP WITH A SETTLEMENT TO THE SAID CASE. sadly, many lupon and barangay chairmen are ignorant of what they are supposed to do in a lupon meeting when parties are at odds, they think they are court but they're main purpose as i've said earlier is tomediate, arbitrate and conciliation of dispute and not to pass judgment of guilt which is the inner working of a court and not of a lupon.