Actually, their primary target was not the Liu Family, but Tang Ming's Minghuang Group. However, since the Minghuang Group was a joint venture between the Zhou Family and the Ma Family, any moves against the Minghuang Group would inevitably meet with opposition from both families.
Now, without external support, the Qin Family, relying solely on Qin Aotian's strength, had no way to contend against the combined efforts of Elder Zhou Zhen and Elder Ma Tong, and there was even a chance the Qin Family could be destroyed.
Therefore, after discussing with Qin Haitian and Qin Haitao, Qin Aotian decided to target the Liu Family first because Tang Ming was the Liu Family's bodyguard and had the closest relationship with them. Eliminating the Liu Family was also akin to retaliating against Tang Ming.