Online harassment by uncle

In early 2014, my uncle played emotional games with my family (including my grandmom, who is his mom). It devastated the family and i had an outburst on email, where i slandered him and asked him to never contact us again. In his entire life, no one had hurt him like I did, because of which he filed an NC against me and threatened to file a case u/s 507 against me. After dozens of apologies from my and my family's side, he did not file. in early 2017, he started to threaten me again with that email which I had written in anger and which I had apologized for a dozen times. He said that he has not forgotten all that and he will still file a case if he wishes to. in 2017, he threated to send an email to my workplace (where my reputation is good, but could be damaged because of all this), he said on email that the foul language i used must be something that i learnt from my mother, and repeatedly kept sending threat emails, saying that he will surely give me a legal answer to my angry email on him. (Lawyers that i have talked to have assured that he cannot file any case on me based on the content that i have written.) Yesterday, he stalked my Quora answer where I had written: "I hate that people stand up for criminals like Salman." To this, he sent another threat email saying that he will share this with Salman Khan (i had not mentioned Khan) and get me arrested for calling someone a criminal although not proven in the court of law. My father is scared of the word legal case and he knows this. Also, since my grandmom (his mom) is scared to take any action against him, he calls her and fights with her and harasses her thoroughly whenever he is upset (which is many a times the case). Her health is falling because of this. I am thoroughly stressed by his behaviour and condescending tactics. I wish to deal with this legally and block him from our lives permanently. Please suggest a legal way of keeping this man at bay. My wedding is coming up in 4 months and since my father and grandmom are scared to take legal action (he knows this), he will surely keep disrupting our peace and cause us mental harassment by crossing several boundaries.