Ice Oni seems to affect based on the will of a person so I think Kaidou might be able to endure it
Big Mom tho, eh I don't know. Sooner or later her hunger pang might kick in which will waver her will.
If for some reason a wound or opening was made that allowed the bullet to pierce through, say for example if Queen landed a shot in an open Kaido or Big Mom wound, then theoretically it should work and would kill them.
However, I highly doubt the force of a gun would be enough to pierce their skin.
Assuming the bullet even NEEDS to pierce their skin to take effect, that is.
If the bullet doesnt need to pierce skin to take effect, yes they would be affected and would probably endure it for a very long time, far longer then the other 2 Yonko given how enduring and durable BM and Kaido are, but in the end would succumb to the poison even if took years to take effect.
Queen is a genius, he has designed these bullets to systematically destroy the human body. They would certainly kill any human who makes direct contact with them, should they be slow and defenseless enough to be tagged.