网友对这个that用法的理解是错误的。

在比较正式的语体中，有时为了强调一个状语，在说了主谓宾或主系表结构后，用and that引出状语。that指代前面说过的主谓宾或主系表结构。例如：

不直接说 I love you very much. 而是说：

I love you, and that very much. 状语very much得到强调。

= I love you, and I love you very much.

《韦氏高阶》就有and that的这种用法：

and that

1 somewhat formal — used to refer to an idea just mentioned

• He was helpful, and that to an unusual degree. 

  = He was helpjul, and he was helpful to an unusual degree.

  
  

网友的句子中，

which rip their own kin in the slightest of need and that too without a sign of remorse.

= which rip their own kin in the slightest of need and which rip their own kin in the slightest of need without a sign of remorse, too.