They are Ghouls:-- (line 88)
Ghouls are legendary creatures that feast on the delicious corpses of the dead. Having ghouls show up in this poem is another way to bring in the hint of death. These nasty little critters thrive on death. It fills them with joy. Their only job in this poem seems to be to help their master spread misery and the fear of death all over the town.
To the sobbing of the bells (line 104)
This is one of many moments in the poem where the bells seem to come to life. In this case they are sobbing, as if they were crying over someone's death. The speaker never tells us that the iron bells of the fourth section are funeral bells, but there's a heavy feeling of death over the end of the poem. Imagine an occasion so sad that even metal bells would cry. That's exactly what we're dealing with here.