We arrived Guangzhou at 14:45 will want to go straight to Yangshuo

You are advised to take a train to Guilin at Guangzhou South Railway Station. The train is available from 7:23 to 20:00, and the duration is 2.5 to 3 hours. The second-class seat costs CNY 137.5; the first-class seat costs CNY 165; the deluxe seat costs CNY 247.5. Then, you can spend a night at Guilin. Afterwards, you may take a bus to your destination at Guilin Bus station for CNY 22. The bus is available from 7:00 to 21:00, and the duration is about 1 hour. Have a great time!

I hope my advice may help you. :)

from Guangzhou international airport to Guangzhou south train station? what is the best way to travel. would Taxi or private transfer be available and how much will it cost we are 8 pax travelling together?

Subway is a good way to go: take line 3 to Jiahewanggang and transfer to line 2 to the South Rail Station directly. It costs CNY9 per person and takes around 70min.

Local taxi can only take at most 4 adult passengers, so you may need two. It costs CNY160-180 per cab. If you wish to travel together, a transfer service is the best choice. It may cost CNY600 or so. I know Travel China Guide offers the service if you are interested. Their contact is traveltravelchinaguide.com by the way!