Su Changfa's capability was unknown. However, he was apparently familiar with secret techniques to do with the soul and adept at hypnotization and manipulation. He was not at all bothered by Li Yao, who was in the 'Core Formation Stage'.
Moreover, he was also the captain of Flourishing Sun. Even Kou Ruhuo, who was in the Nascent Soul Stage, showed enough respect for all and addressed him as 'Master Su'. Therefore, his Cultivation could not be very low. By the most conservative estimation, he should be in the middle level of the Nascent Soul Stage.
The middle level of the Nascent Soul Stage and skilled at the secret techniques concerning the soul—he would prove to be a tough enemy in a fight!
Tang Qianhe was the only one who seemed weaker, but she would not be lower than the middle level of the Core Formation Stage and was probably at the peak of it!