My sister is not following my mother's will properly and doesn't even have a death certificate yet what can we do being a son

You need to take your morther's will to a competent local estate lawyer IMMEDIATELY and hire him or her to file the will for probate.  Tell him or her what your sister is doing.  In the meantime, advise your sister that her power of attorney expired and became inoperative at the moment of your mother's death.  It is no longer valid for any purpose and it no longer gives her any power whatsoever over your mother's affairs.  She is not authorized to take anything from your mother's belongings, and that includes bank accounts and safe deposit boxes.  Do not delay.  Your sister may quickly place valuable items beyond your reach. Good luck with it.  Sadly, this sort of situation is not uncommon, but an experienced lawyer will know what to do. WARNING:  I am not your lawyer and providing you with the generic information, definition, clarification or explanation you seek about a legal matter on this anonymous forum does not make me your lawyer.  By answering your question I am only trying to provide you with general information that will deepen your understanding of the legal concept that appears to be an issue for you, that will hopefully guide you in selecting and communicating with a lawyer of your choosing.  The reason for all this is that legal problems are intensely fact-driven, and it is impossible to give anyone correct legal advice without comprehensive inquiry by the lawyer into the specific facts of the situation that concerns you, and the law of the jurisdiction in which you reside, and that is impossible to accomplish through this website.  Even though I am not your lawyer, if I should later become your lawyer no representation is made that the quality of the legal services to be performed is greater than the quality of legal services performed by other lawyers.