First of all, I hope your family members are recovering.
I may be naive but I would have expected the cruise line to have postponed/delayed the cruise. Wiser, more experienced American cruisers will no doubt tell me why this would not have been done.
Like yourself, I would be VERY angry, never sail Princess again and consult on what options are open to you re the recovery of the cost of the holiday and additional expenses.
I know I have a very simplistic way of looking at things, but if I had a reservation at a resort hotel where a similar outbreak had occurred within the same timeline, I would expect the hotel management to inform me and allow me to make alternative arrangements - why should a cruise line be different?
In the UK, for the hotel scenario - the hotel would close until the authorities were satisfied that the problem no longer exists.
Please keep us informed.