MTR from hongkong to Guilin

Yes, your route is right. Take the MTR to Lo Wu Station, and pass the border, you will reach Shenzhen. From Luohu Station, you can take the Luobao Line to Huizhan Zhongxin Station, where you can transfer to Longhua Line to Shenzhen North Railway Station. In the north train station, you can take the bullet train to Guilin.

Harry is way is fine. You can also depart from TST to Lok Ma Chau, which is the terminal station of East Rail Line. Upon getting off, cross the border to Futian Border. Nearby you can directly take Longhua metro line to the North Train Station to catch your high speed train.

Or here is a direct way, but it costs a little more than train:
in the left of Marco Polo Hotel, which is close to TST MTR Station, you can take a direct cross-border coach to Shenzhen North Station.

Thank you Harry!! Do you know about how long would that commute take?

Hi Mona, thank you for your help! Do you know which is the quickest way? We don't have much time during this trip and I am trying my best to plan accordingly. Thank you for your help!

From HK to Shenzhen North Railway Station, it takes 1.5 to 2 hours. About taking the bullet train to Guilin North Railway Station, the duration is about 4 hours.

Well, the quickest and the most convenient way for you is to take the direct cross border coach to get to Shenzhen North Station. Then transfer to high-speed train to arrive in Guilin.