So... the MC move "Inflict harm as established" and the harm that a PC gets when they choose to "Seize something by force" (a player move) are different things. And in neither case does it matter if you're taking harm from multiple sources/directions or not. All that matters is if you're taking harm from one or two dudes, a small gang, a medium gang, or a larger gang. Those are your choices!
If you're using the MC move "inflict harm," then you inflict harm based on the weapons and size of the person/group doing the harm.
If the player is "seizing by force," then -- doing this from memory -- they inflict their harm (based on weapons + size of their gang, and +1 if the player chooses "inflict terrible harm") and take harm from their opponents (usually 2 harm + size of their gang, and -1 if the player chooses "suffer little harm"). That's it.
AW isn't gritty and representational, mechanically. All the grit comes in the fictional description of how it goes down. If you want to make custom moves to do it differently, you can, but that's how it works, by the book.