It is not lawful to take one’s wife back after one has given her three talaqs. The holy Quran says:
فَإِن طَلَّقَهَا فَلاَ تَحِلُّ لَهُ مِن بَعْدُ حَتَّىَ تَنكِحَ زَوْجاً غَيْرَهُ [البقرة : 230]
Three talaqs are complete talaq which is called mughallazah (irrevocable) which terminates the relation of husband and wife and both become haram for each other. It is adultery for them to live together. The family members and people of locality should stop them from living together and should separate them. If they do not accept it and continue in the same state, you can boycott both of them so that they can reform themselves.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband