Train from Kunming to Lijiang

The child under 150cm can buy the child ticket with a discount about 25% off. There is no such cabin for 2 people on this route. You can choose soft sleeper for 4 people, or hard sleeper cabin for 6 people. K9682 and K9686 sometimes have a special room for 3 people.

I also want to buy an advance ticet. How can I buy it without any expensive surcharge?

As long as you book from an agent, there would be surcharge. You can make a selection between them based on the price and service. If you had any friend in China etc they should be able to do it for you in advance.

I see. Is it possible for me to buy it on the spot, just after I touchdown the Kunming airport? I planned to take train on the night, the same day I arrived. Can I buy the ticket at the airport?

It is OK to buy it on spot, but it owuld nto work at the airport. You need go for the railway station instead. It would be better if you check the availability online often like on this website. If you found it only limited amount left, i guess you need to buy online instead.