How do I become DPOA?

How can I proceed with taking over my parents finances when my mother is irrational, has beginning dementia, undiagnosed untreated bipolar disorder, my father has checked out emotionally and mother will not agree to my brother or myself becoming DPOAs? My brother and I can no longer keep supporting her spending sprees that leave them short for their rent. Not only has my brother had to short sale his home a few years ago but our parents had to file bankruptcy and sell their home. We have made multiple attempts to get her the medical attention she needs, but she always relapses. We were finally able to get her in to see a psychiatrist, but no one in the medical office will discuss her case or plan with us because we are not on her hipaa. Mother refuses to allow us to be in the room or discuss with us. Did I mention my dad has checked out and does not care anymore? He deals with her by letting her do what she wants because it's easier to avoid fighting with her. This is how he deals. My father is also 3 months post op from open heart surgery. Any guidance would be appreciated. Mother is mentally incapable of being in charge of their finances or her medical care.