life - How to deal with your in-laws on holiday?

Chinese are already flooding Europe as tourists, but this gets an extra dimension when it concerns your own in-laws. Tomorrow my mother and sister in-law from a trip through Europe. Since more of my readers might face that dilemma - both a pleasure and an ordeal - some tips might be in place.
We first feared that the rather rigid migration laws in Europe might stop them from coming all together. Not only did we have to fill in two times one kilo of ludicrous forms, there were deadlines we all missed. Nevertheless: both got their visa. Then they announced they wanted to stay for three months, a bit of a shock, since we both are pretty busy and they would not really like our busy life - without them. Then, it showed that my sister in-law could only leave her company in Shanghai for two weeks, so that reduced the pressure a bit.
We then organized them a two-week trip through Europe: there are already abundant travel organizations offering such a kind of service. I missed their arrival since I had to rush off to China at that time. Now I have the rest of the week to debrief them: what country did they like most, and why? What could be done better, what did they dislike? Should be interesting stuff for many people.