Divorce Support Forums: Parents unable to live together

Both of my parents live in Hawaii and my sister and I live in another state. My father is sick and my mother has a degenerate disease which limites her mobility. My father has been a control freak for their entire marriage and things have now gotten worse. We are bringing my Mom to live with us as my Dad has said he no longer will care for her. My parents have a savings account and checking account with both of their names on it and my Dad has a pension savings account with only his name and my Mom as the beneficiary. My dad has told my Mom that she is "allowed" to take only 1/2 of the savings. Well all of my Mom's income (SS and small pension) goes into the checking and then all bills are automatically deducted each month. My Dad's SS check goes into savings. I do not think it is fair that my Dad is saying that she can only take 1/2 of what is there now while all of my Mom's income continues to pay for the living expenses of the house she no longer lives in. I'm not sure if they are heading to divorce, but I want to know what rights my Mom has in regards to access to finances needed to support herself. Help!!