Can I send a defamation warning notice via a lawyer if I'm abroad

I am currently living in the UK. In 2009, my daughter had married a guy in India in 2009. After a month and a half, me and my family had to return back to the UK but my daughter stayed with her husband for a short while. In our absence the husband along with his parents hit my daughter and forced her out of the house in the middle of the night. My cousin then made her come back to the UK after we arranged an emergency flight travelling for her. Following that along with his sisters, family and cousins, etc. they sent my daughter a divorce (muslim). We didn't issue any legal proceedings against them before or after, despite their outrageous behaviour of asking for dowry during the marriage. The guy now has two identities in two towns of gujarat (first in Valsad, and new one in Daman - due to the Portuguese passport claims). He is also married and has a son. Even though they are no longer connected with us they are defaming us which is causing many marriage proposals for my daughter to break. Whenever, we receive a marriage proposal they contact the boys side and defame my daughter horribly by slandering her character and such, which leads to the end of any relationship. I have contacted the police in India who told me that I would be able to send them a warning notice if I make a police complaint against them and if they still don't heed to the warning - further action could be taken. I wanted to know whether I have to be there in person to issue the complaint or can I send this via a lawyer in India? Also, what claims can I make against the boy's family?