Sometimes my father, my mother or I involve in a discussion in which we discuss about Islam, the authentic agreed upon hadiths and the rulings. As we are living in a so called Hanafi area, being the follower of the authentic hadith-based Islam (back then we were the same as them but when Allah gave us the true understanding of the religion), we differ in many believes, practices and appearances with them obviously, often refer to us as deviant, odd and sometimes they start arguing with us though my father and I never tried to engage in those arguments even though once I experienced a very bitter and slandering from them in the inside of the masajid! Anyway we are mature enough and God fearing; overtime, we got used to it and they also got familiar with our ways of offering Salah and the like, so we don’t bother about it anymore. But the sorrow fact of the matter is that my brothers (2 elder brothers) don’t pray at all (sometimes they go to masque with their friends, in ramadan they mostly become good person and try to pray and observe fasting), sometimes they even hesitate to do Islamic practices, one of them has declared himself an atheist ; in the past, the atheist one oppressed us, mainly my mother, in many heinous ways, I don’t want to bring those memories here, but recently the elder one is also nagging, arguing, neglecting, slandering, mocking the things we (my old and ill father who's now main cherish is to achieve the Jannah by the level best of his ability and I also encourage, help and talk with him about various matters of Islam) belief and discuss among us (me, my father & mother); he questions things that have solid evidence in the Quran and Sunnah out of ignorance or for reasons I do not understand, and recently he's trying to differ or argue with us in every discussion we make about Islamic rulings.
My father displease with them, me too.
So my question is : How should we deal with them when it comes to Islamic clear cut truth and the like (i.e. the ways of praying that we find in the authentic sunnah, Aqidah etc.)?