Two notices with a time gap of one month sent stating Talaq to my sister

Actual scenario : My brother in law sent two notices one on june 12,2021 and other on July 12, 2021 saying talaq to my sister. In first notice he has clearly mentioned that, if want to rejoin she can come to him with an intention of living peaceful life. My sister tried to rejoin the family immediately after first notice but he did not accepted and handed my sister to police saying she is creating newsense by coming to home and further he saying to police that he has given notice legally and will decide the matter in court. In second notice also, he has pronounced talaq and said if want to rejoin she can come to him for which remarriage need to be conducted as per Islamic law. when approached to him, he was saying he is not interested in remarrying her and again handed to police station. Also the two child one girl of age 12 and other boy of age 10 is under his custody. My sister is not interested to give divorce as she can not live without children. My Question : How can we stop my brother in law from pronouncing third talaq. Is there any provision/section in law by which we can declare the talaq invalid.