I am on a lunch break and don't have time to read all the posts (will do when I get home!) but wanted to express to the OP how sorry I am your sister and family lost their valuables.
Theft is never nice, regardless of what, where and how. Someone has gone through your possessions and it's not a nice feeling at all.
It hardly compares but on our last visit to AKL we also experienced "theft" - to me, theft is taking something that does not belong to you. If it is taken by mistake, it can be returned with an apology, when it does not return, to me it has been stolen. We were supposed to be in a
DVC studio and were moved on the 1st night to a regular lodge room because the room was unclean (towels and toiletries used, rancid food and bugs on the counter). We prefered a DVC studio but had no choice - and with the lodge room came daily mousekeeping.
I always take my huge bath towel with me because I love it and it's big! It's blue and white with embroidered fish on it and so not a Disney hotel towel. Still didn't stop housekeeping taking it (either deliberately or by mistake). It happened on the last day of a bad week at AKL - nightmare stay, and was the final straw. Front desk were rude and unhelpful. Housekeeping didn't want to know.
In the end I ended up going down to the front desk and asking for the manager. I was unwell and supposed to be resting but whatever! He was disgusted with everything that had happened and worked hard to fix a lot of things. We're still in contact with him now - he was so nice.
Our rules for our valuables now are this - we use the safe for everything such as laptop, cards, keys for home, my jewellery and our money. Anything bigger like my perfumes, our pins or new expensive purchases (trainers etc) we lock in our suitcases. Our suitcases are hard and both combination and key or magnetic lock. We have a long bike lock and we lock all the handles together. Hope it works as a deterant - would be difficult to try and get all 4 suitcases out quietly locked together lol!!