Hard problem because we will never know how their minds are thinking. Obviously something about being in a cat hotel so close together has made them act differently. Imagine being in one room with your best friend for 2 full weeks and not being able to get away for private time. There is a good chance that you would end up with some sort of argument.

Now on to how to fix it.........I am really not sure we as humans can help them. I feel time will heal all wounds. But in the mean time, try hard to include them together in many activities. Feeding treats, playing, petting. Do these things only if they are together, so it seems as a reward for them being together. At the same time, make sure there is no reason for rivarly. Make sure they do not have the need to "fight" over space, food, litter boxes, attention.

Best of luck. I know how close they were and it is very sad.