They weren't on the porch though.
It was weird, they were essentially killed for sport. The only part of them that was eaten were two of the heads. The rest of the bodies were intact. I'm thinking racoon, or a wild chance it was an owl. These were fully grown birds though, so I doubt it was an owl.
Most likely an opossum did this. They love eating the brains.
Owls could definitely take a chicken though. Great horned owl could take a full grown fox if it wanted. I once had a Cooper's Hawk take an Americana/Easter egger, and a Cooper's hawk is about 1/3 the size of a Barred owl, so, Barreds and Great Horns could easily take a chicken. Great Horned Owl's MO is to decapitate it's victims because it is the fastest way to minimize the risk that the prey will fight back and injure the owl, but usually they will leave the head at the sight of the attack and carry off the body to eat. So, if you found a mostly intact chicken carcass with the head chewed on and brains eaten, it was likely an opossum; if you found a mostly eaten headless chicken carcass, that was likely an owl.