people - I'm looking at WotC and Paizo writers in particular - who don't seem to know that there is no such word as 'foes'. Foe means enemy, singular or plural, dagnabbit!
Where on earth did you get that idea?
About five seconds of googling or the consultation of any reputable dictionary would have disabused you of the notion.
This might sound familiar, as well:
Two households, both alike in dignity,
In fair Verona, where we lay our scene,
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean.
From forth the fatal loins of these two foes
A pair of star-cross'd lovers take their life.
While the word "foe" can refer to a collection of people, it doesn't follow that there cannot be multiple foes. It's like claiming that the word "armies" doesn't exist because one army can be made up of many people.