Only Boa joined. And she obliterated every marine there right that instance. The Kuja fodder were the ones battling the Seraphim.
Do you have ANY proof for that second attack thing targeting coby?? We don't even see her using her first attack at all. That might as well be a no name move were it not for the fact that we already knew its name and what it looked like. A move she used against literal canon balls lol. So it's not a great feat for coby to dodge it either.
Her sisters literally stated that they fought it we saw them brushed up on panel. They also stated that they were unable to damaged it. They contributed nothing.
Cool boa showed up and fodderized every marine except one. Which contradicts your notion of coby being fodder. Not only did her ability fail on him she then decided to attack with another named attack
The same slave arrows turned cannon balls (inanimate odjects) into stone. So the "coby isn't attracted to woman" excuse don't work since it's been shown to work on objects that have zero feelings lol. Her perfume attacks are always only kicks. So we know she was about to physically attempt hitting coby