For power of attorney over whom? A parent, I presume. The short answer is that you can challenge anyone for anything you want. The long answer is that if the parent in question specifically named your sister as POA while that parent was of sound mind and that parent is still competent and mentally sound and your sister is carrying out her duties as POA properly, then you probably will lose. You'll only win if you can either show to the court that your sister persuaded the parent to sign the POA over to her while the parent was of unsound mind (thus nullifying the POA) or if you can show to the court that your sister is not acting prudently as a POA. By acting prudently, I mean that she's not properly attending to the legal affairs or medical needs of the parent, spending the parent's money in an improper manner, that sort of thing. The law on this differs from state to state, so I can't be any more specific without knowing where you are.
Of course not! A power of attorney must be granted by the person, it cannot be taken without a court order.
That would be most simply done by granting a Power of Attorney.
You will need to see an attorney, have you sister diagnosed by qualified medical professionals, and seek the assistance of the courts.
No, your permission is not required. Your father can grant those rights to anyone he wishes.
Your parents own the property. What they do with it is up to them. Your power of attorney doesn't stop them from doing what they wish, or what they are convinced to do by someone else.
You first have to authorize a power of attorney form, then make them sign as the 'Principal' and you should sign as the 'Attorney-in-Fact' If your parent is competent their grant of a Power of Attorney must be voluntary. They must execute a Durable Power of Attorney document that names you as their attorney in fact. You and your parents should consult with an attorney who can review the situation and advise you of your options and the consequences of executing a power of attorney. If your parent is not legally competent then you must petition the court to be appointed their legal guardian.
A POA expires when the principal dies. They have no power over the estate or the beneficiary.
You would apply for it at the probate court if she is unable to grant it. The courthouse can provide the required forms and list of documents necessary.
Yes. The POA expired at the moment your mother died. Your sister has no power over your mother's assets. You need to petition the probate court to be appointed the executor. Once you have been appointed you will have full authority over your mother's assets and the settling of her estate.
A power of attorney represents a living person. After their death, the power of attorney has no power to do anything, the executor takes over.
Ask one of them. Other than that there is no other researchable way. Such documents are not generally required to be filed with the public records unless there is real estate involved. In that case a copy of the power of attorney would be recorded in the land records with any transaction that affects the real estate. On the other hand, if your sister is mentally disabled she may not be legally capable of executing a valid power of attorney. If that is the case a legal guardian would require appointment by the probate court and you should discuss the situation with an attorney who specializes in family law and probate.
No. A POA cannot be transferred from the holder to another individual. A new POA or guardianship order will have to be obtained through the required legal procedures by the person seeking such.