I'm sorry to hear that you and your family are facing this difficult time.
If it's possible can you coordinate a visit to their doctor? Explain to the doctor before hand why you're coming in and how he/she can assist you with the message to the family member, and that you will be accompanying them. With the GP the message will carry a bit more weight.
Think of it this way. They're not losing their freedom, just reducing their mobility. Hopefully family can pick up the slack.
Best of luck.