Me and my sibling have no contact for over a year,how do I get around not needing 3 signatures for my mothers cremation, she has Alzheimer's not decea

If you are her POwer of Attorney you could try doing a prepaid funeral that would include cremation.  Unfortunately, the cremation service may still want to see either consent of your siblings, or that your mother had appointed you as her funeral representative.  There is a form that she could sign giving you the authority to arrange for the cremation, if she was capable of signing.  You only have to use the following langauge:   "I hereby nominate, constitute and appoint [insert name] to serve as my Funeral and Disposition Representative, pursuant to P.L. 2003, c. 261. My Representative shall have the authority and power to control the arrangements for my funeral and the disposition of my remains. My Executor shall notify my Representative of this appointment, and shall advise my Representative of the financial means available to carry out the Funeral and Disposition arrangements. In the event [insert name] should predecease me or for some other reason not qualify to serve as my Funeral and Disposition Representative, then I nominate, constitute and appoint [insert name of alternate] as my Funeral and Disposition Representative.”