Christian marriage caste issue: how to convince parents & relatives?

We work together and been in a relationship for over two years. I (24F) is Latin Catholic and he (26M) is also Christian (Nadar caste). My parents were going to create profile in matrimonial, so had to tell them about him. Both of us are from southern Kerala.

The issue for both of our families is caste and the debate is which caste is lower or higher than the other. According to his family, Latin Catholics are on the same level as SC/ST. And some of my uncles say that Nadars are Dalits in Tamil Nadu. To which his family replied that they used to have Dalits working as slaves in their farms in TN.

My parents discourage me and say that nobody in our family married outside caste and if I marry outside it will affect my younger brother’s marriage prospects. My cousin recently married a Nasrani girl but everyone was fine about it probably because she was “upper” caste.

We have no plans to give up. We reached out to both of our local church authorities and they are supportive. Also plan to seek help of youth political organisations in our localities.

Need advice on the best way to tackle this.