My sister adopted twin girls and now the two girls are misrepresenting themselves as my 92 year old mother's daughters.

The two girls have taken over my 92 year old mother's property and are living in her home which my father and mother bought in the 60's. I tried to see my mother after she had surgery at Kaiser Permanente in Downey, CA but the hospital will not give me any information because they say my sister has legally excluded me from seeing my mother. I would like to know how my mother is doing. My husband was caring for my mother and her property (home) until my sister has somehow excluded he and I from her life. What can I do?