Doc Scratch probably isn't behind the monsters. He's never used monsters before, they're not his colour scheme, and he'd be more likely to verbally manipulate Joey. Plus, the monsters appear to be trying to STOP Joey getting to the attic (they cut the power, one blocks the stairs in the group strife, and if they catch her they eat her) and Scratch secures her connection and acts as the hint function, implying he wants her on Alternia. So it seems there are two big bads involved...?

The monsters obviously come from the neighbours.