My brother has been given POA for my dad. Must he show this to the rest of family or can we get a copy of it somewhere?

My daughter moved, at the request of her grandfather, from Alabama to Texas to help care and be a companion for her grandfather. My brother, who says he has power of attorney, has given her 3 days to move out. He has also refused to talk to me regarding the medical condition and other issues of dad. My dad also signed to give me title to his car which my daughter is using to drive to work. While my dad was visiting me he requested to see a lawyer to insure I receive 3 pictures, 2 end tables and a corner shelf when he passes. I drew up the document, which also included request that my daughter have authority to sign medical documents in the event my brother was not available. I took my dad to judge's office where they read the document to him. He was questioned if he understood and that this was what he wanted. The document was accepted and notarized. My brother says the document is worthless because he did not approve and that I forced my dad to sign. My brother has sent letters to my daughter, husband and I, rescinding everything my father requested. Can he do this? The letters he sent were not witnessed nor dated, though signed by my father and brother. I know my father would never say things listed on the letters. My father does have slight alzheimers now and is quite frail. I fear that I shall never see my father alive again. He lives alone in his own home and is 600 miles from me.