Can a person or business refuse a POA?

Can a person or business refuse a POA?
Can a person or business refuse to accept a Power of Attorney? Does a POA have to be professionally done? Or could I type something up and have a witness sign? Does the person I appoint POA have to sign it or just a witness? Does it have to be notorized? Thanks for any assistance you can give me.

Wills & Trust My 94 year old dad married his caregiver and has subsequently died.

Wills & Trust
My 94 year old dad married his caregiver and has subsequently died. All his assets were apparently put into a trust in her name. She has cut off all contact with his family. How/who do we contact regarding his will and/or the trust? Can a trust be contested? Since she refuses to to speak to us, we are in the dark. My sister had power of attorney as well as being executor, however, when the caregiver married dad, all power as well as financial information shifted to her.

Add Name to Account w/o Notifying POA My Dad has Power of Attorney over my…

Add Name to Account w/o Notifying POA
My Dad has Power of Attorney over my Grandfather for the past 5 years. Recently my Aunt has added her name to my Grandfather’s account and has also gotten a debit card in my Grandfather’s name. Can the bank do this without the approval of the Power of Attorney?