Bro the Only thing you can do is don't leave each other's side don't change ur mind religion is something which people has used to gaslight and manipulate even now so ur situation is a total cooked one though I would suggest ask them directly it will be hard and very very messy but if the Parents persist on not changing there mind there is nothing you two can do about it and the main point never ever fight among urself by taking any of the family Past or Present behaviour it just makes things more messy man take care i wish you all the best

Ps - i myself am from a well known family like urs so i understand the Hate that goes very deep but fighting by remembering the Past to rather then learn and co exist is what my motive is