Connecting via 2 chinese towns

Hello. Can you help me please:
Do I need a visa if I'm flying Bangkok-Guangzhou-Beijing, but not leave the airport in Guangzhou, just transfer on flight to Beijing (3 hrs wait but inside). And then in Beijing i have 1.5 days, before fly out of China direct

and if its ok to stay inside airport, not pass Guangzhou customs, but only Beijing customs - qualify for free transit?

Same work if fly Bangkok-Shehzhen-Beijing or another Chinese city?