这是个并列句,因为有but将两个句子连起来.
none of them在这做主语,是正确的.
none of whom在这相当于定语从句的引导词,一般用在从句当中.
上句可改为：They were all very tired,none of whom would stop to take a rest.只是将but去掉,逗号后的部分要么是个短语,要么是个句子——若是句子,则需要引导词,如none of whom；若是短语,则将后半部分的谓语去掉,用非谓语指代动作,如They were all very tired,none of them wanting to stop to take a rest.
在英语的句子里,两个句子要是用逗号连起来,就必须要有连接词（and,but,or,though,although,then等等）或引导词（when,where,why,what,which,who,that等等）
用连接词连起来的句子是并列句,用引导词连起来的句子是从句.
回答完毕,