Perguntas sobre 'mamãe'

Yesterday I watched the Netflix movie "Mama". After watching again I still don't understand why the dad was in panic at the beginning, and what happens to the girl's mom. Why did he then try to shoot himself or the daughters? Did I miss somethin...

In those works where zombies or vampires (or other undead) aren't merely victims of some weird and exotic disease (and still biologically alive), what traits do the undead have that are common across most? Are any other explanations offered as to...