transit for 2 hours from Bangkok to Khartoum with confirmed Tickets of SV

Hi we will travel from Khartoum to GUANZHOU for 4 days (we have visa for that)then will go to Bangkok for 4 days as well ,on the return will come from Bangkok on Southern china airlines to GUANZHOU (no transit G)and we have confirm Tickets to Sudan on Saudi airlines .do we need a transit G?