In the fourth chapter of George Orwell's Animal Farm, the human beings return and try to retake the farm from the animals. We are told that Farmer Jones and some of his men were among the attackers, as well as "half a dozen others from Foxwood and Pinchfield." Mr. Pilkington is the owner of Foxwood, so we might assume that he participates in the battle, but I am not finding any explicit reference to him in Chapter 4. Mr. Frederick runs the Pinchfield Farm, but, again, I'm not finding any specific reference to him in Chapter 4. Still, I can see how one would assume that Mr. Frederick and Mr. Pilkington would be present at the Battle of Cowshed.
Most of Orwell's narrative in this chapter deals with the difficulties the animals had in battling against Jones himself. Orwell does mention "a stable-lad from Foxwood", whom Boxer ends up killing, albeit accidentally and with great remorse.
"He is dead," said Boxer sorrowfully. "I had no intention of doing that.
I forgot that I was wearing iron shoes. Who will believe that I did not do
this on purpose?"