Fathers extra affair after mother's death

It's been 10 months since my mother's death and my father is already in a relationship with another woman, who also happens to be a widow with a son and a daughter. I am currently 19 years old. My father plans to bring her to our house without marriage and actually keep her as a maid to fool the world, but I have enough concrete evidence to prove the real situation. Somehow or the other I don't want to get involved in all of this. All I want is him to pay for all my requirements till I get a job (roughly 4-5 years to finish my grad) . Also I want to completely separate myself from these people. I want legal help so that he , his second affair and their children do not later come to me for any claims, even after his demise , if so may happen. I do not want any share of his property or his possessions. I just want to secure my future .Can someone please help me?