How do you deal with someone in your family having mental illness?

How do you deal with someone who always refuses help and who blames everybody else and sees nothhing wrong with their unstable behaviour. How do you deal with someone who enanles their behaviour and doesn’t do anything at all to get the person treatment. I’m so sick of this person in my family who never does anything at all to help this person. I know I can ‘t force this person to get help but I don’t know what other options there are because I can’t live with this person at all and yet I am forced to.