Bus tickets from Guangzhou to Yangshuo and Yangshuo to Guilin.

We need 4 bus tickets from GZ to Yangshuo and Yangshuo to Guilin. Would you please tell me where we can buy the tickets in GZ? And also the bus from Yangshuo to Guilin, can we buy the tickets in GZ? Pls also advise the costs of each destination. Thanks alot.