Property jointly owned by siblings

[Drewpin]

What is the name of your state (only U.S. law)? New York State, My sister has taken my elderly mother to live with her. The house is in the siblings names with life use by my mother. However, my sister has taken it upon her self to empty the house. She has removed and disposed of all of my mothers clothes and let her children go take what they want. My mother is suffering Alzheimers and has no Power of Attorney that we know of. Is there anything the rest of us siblings can do to stop her from getting rid of everything?