wet food vs dry, cat-sitting for my sister's cats

I have been cat-sitting for my sister's two cats for a month while she is on a work contract in Chiang Mai. They are on mostly dry food and she asked me to keep the same, but one of them stopped eating properly by day 4 and I panicked a bit. I tried a small amount of wet food, which she only had as a treat before. He ate it all within a minute. I know that does not mean much on its own, but it made me think about what the usual advice says. From what I read and from talking to a friend who is a vet nurse, the big difference is water. Wet food gives more moisture, and dry food can be good for teeth and easier to leave out all day. Most people do a mix, which is what my sister does at home. The rule she gave me was simple. Keep the same food for the first days when you look after them so you do not change two things at once. Then if you want to change, do it slowly over one or two weeks by mixing a little more each day. Don't throw out the food after an hour if the cat is not hungry, it goes bad fast in this heat, so just put it in the fridge and make a smaller amount next time. The cat is fine now and back to normal food. I will be happy when my sister comes home.