First let me say, that I'm sorry about your relatives health, and the situation, you have found your self in.
Sadly, the conditons, are what they are, and have been in place for a reason, while we may not agree with, it makes business sense.
I wish they sometimes could go on a case by case situation. but, it's better to realize, this probably won't happen.
If you go on the cruise, with the attitude you stated, you will be cutting your nose off to spite your face, as my Mom would have said.... sailing as angry as you are, right or wrong, will make for a miserable cruise for all of you. The story will be retold by you, many times onboard, I am sure, and that will fuel your anger even more.
Might I suggest you make alternate plans, get your refund, and cruise when you all are in a better frame of mind. I hope all goes well for all of you.