Ye Hongfeng must have dug the tunnel as a backup plan for a situation like today. She must have planned for it more than half a year ago!
Based on Ye Hongfeng's intelligence, she would not have thought of such an elaborate plan. Besides that, she would not have risked her life to save Long Siye. The only explanation was that either Long Fan or the Omen were controlling Ye Hongfeng's body.
It would be impossible for a normal soul to possess someone else's body. Though Ye Hongfeng's cloned body did not have a master soul, it was made using the genes and cells from the real Ye Hongfeng. Thus, its magnetic field was similar to its master's, and only a soul who possessed similar traits like its master's could possess its body.
However, Ye Hongfeng was able to control the cloned body and possess Gu Xijiu's body at the same time as her soul was somewhat unique; perhaps, Long Fan had modified it before.