这种情况就是你该查词典的时候。

《韦氏高阶》ditto : adverb.

informal

— used to say that whatever you have said about one person or thing is also true of another person or thing

• Boston is getting a lot of rain. Ditto New York. [=New York is also getting a lot of rain]

• He is good at baseball, ditto at golf. = He is also good at golf.

所以你的句子：

Lila is dead. Ditto three girls and one boy. 

= Lina is dead. Three girls and one boy are dead, too.

你的第二个句子中，ditto的理解要参考前一句话。