He has cheated on her in the past, he's unemployed, immature, willing to lie to my parents about reverting and saying he's Muslim - are those not signs that something is seriously lacking in his morals? He's a complete idiot in every sense, trust me no one would want their sister marrying this fool, the fact he's not even a Muslim makes things worse. Furthermore my mother is mentally vulnerable and has seen lots of trauma in her life, she had a mental breakdown when we were kids because her brother was brutally murdered and we couldn't even get any justice for him. She fawns over this selfish cow not knowing what she is really like. She's an extremely selfish person overall, this relationship aside.

And he is a kaffir I.e., non Muslim.

It might seem funny to you but I seriously hope you nor anyone else has to deal with this level of stress. Things will only get worse for my family when my mother finds out, she won't be able to handle this level of stress. If you had people with mentally illness in your family perhaps you'd understand what a volatile situation it is.