I don't know specifically about Mississippi law, but it is highly doubtful. Probate Codes typically are clear about the requirements of a Will, which require action on the part of the testator (person making the will). For example, it must be wholly in the testator's handwriting, or, if not, signed by the decedent or by someone at his direction in the presence of two (or more, depending on the state) witnesses. A power of attorney is usually drafted with general language which I don't believe would be construed to be specific enough to reach the conclusion that the brother signed the document at the decedent's direction.
You need to speak with an attorney as soon as possible. If your mother is legally incapacitated she cannot execute a POA document nor can she change her will. You need to petition the court to be appointed her guardian so that you can take care of her, her assets and protect her from predators. You should consult with an attorney who specializes in elder affairs or probate. Do not delay.
Absolutely Not!
No, the words "mother" and "bother" do not rhyme because they have different vowel sounds.
The only person that can change the will is the person who created it. There are ways of changing the outcome of things. Consult a probate attorney for help.
Lazar was the brother of Mother Teresa.
Other, mother,
If you mother is of sound mind and can speak for herself then tell her you don't want to be Power of Attorney. If your mother can't speak for herself and there is another capable person to carry out this duty then change it through a lawyer.
see links below
If your mother grants you the power of attorney. Otherwise it will require a court order.
brother, mother, bother, another,
bother, mother, anther
You need to file an emergency change of custody with supervised visitation. see links below