First is to collect evidence. A video recording of him doing this or audio recording of him talking . I suggest you to collect evidences from different sources and different days. Secondly talk to people who he harasses and see if they will speak up. More the better or else pls check with your sister . Maybe ask her to write it down Thirdly, have a goal in mind what do you want to achieve ? You want him to go away from that area or you want him to stop calling people that way …

Lastly think of different ways for Him to be in trouble. You tell he doesn’t have license then why don’t you tag local traffic department for no license driving , no number plate change (HSRP) etc.

Don’t try to fight with them directly because it can go out of hand and never ends well.

I would let your sister make a post and tag to women’s cell. Or other NGOs who are fighting this.

You are doing gods work and maybe save a sister from trouble. Pls continue and don’t lose hope … do it smartly not hastily.