Am I legally responsible for paying for my mother's care in my sister's home.

My mother recently moved in with my sister & her husband. My sister's husband is demanding that me and the other siblings help him pay his mortgage, utilities, and compensate my sister for caring for my mother since she will have to stay home. My mother is already helping them with her social security check and she has insurance to cover all her medical needs. Am I legally responsible to help them finacially? - Is this your question? Add additional information