The amount of smoke from 4 fire pits is negligible as far as respiratory issues go. Again, no one is burning industrial grade coal furnaces, and the way you talk about the fire pits it sounds like you're picturing late 1800s London, not a handful of spread out small fire pits in an open area. And for the same reason the amount of ashes is gonna be negligible (not to mention that they might run on natural gas, as you said).
It feels, to me, that this crusade has more to do with the possibility of these attracting "undesirables" to hang out than with anything objectively bad with the fire pits.