Replace "who(m)" with a pronoun. Which one sounds better?
. . .
who/they attack everything around them.
. . .
whom/them attack everything around them.
Note, the verb is "attack", its object is "everything" and its subject is "who". Use "whom" or "what" for the verb's object:
Object: non-person
They attack
everything. =>
What do they attack?
Object: person
They attack
us. =>
Whom do they attack?
Grammar Help: I think that
whom should be changed to
who.