Answer:
(Fatwa: 712/500/L=1431)
(1) Anyone from husband and wife can sign first; since the demand of khula is from wife hence she should sign first.
(2) If both husband and wife agreed on khula and they signed khula paper, talaq took place, the signature of witnesses is not necessary.
(3) Yes, it shall take place.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
