What can we do to ensure my sister's safety before returning?

After marriage, my sister and her husband quarrel frequently over their own parents because her husband and his parents always insult my family (the girl's side) by saying we are not giving this or that, and they always make false allegations against my parents, even after we gave everything. This is the reason my sister and her husband fight and argue. After 4 months of marriage, my sister came back to our house for the first time to visit, but after a few days, they started insulting my parents (the girl's side) again. Now, after 1 month of this incident, they haven't tried to call my sister. My sister wants to give another chance to her husband's side, but we (the girl's side) are worried about her safety because we don't think she will be safe there. We want strong advice regarding the safety of our sister, as they have not called her for 1 month. We are still trying to contact a mediator to talk (both sides: the boy's side and the girl's side). What can we do regarding her safety before my sister goes there?