The day before cooking, dry-brine the chicken: In a small bowl, stir together the paprika, black pepper, cayenne, and salt. Puncture the lemons all over. Place the chickens on a sheet pan, put the lemons in the cavities, pinch the skin together, and use toothpicks to pin shut. Rub the paprika mixture all over the chickens. Refrigerate uncovered for 12 to 24 hours or leave at room temperature for 1 hour if short on time.

Heat the oven to 300 degrees. In a medium bowl, toss the potatoes with 2 tablespoons olive oil and season with salt and pepper. Place the potatoes around the chickens. Drizzle the remaining 2 tablespoons olive oil over the chickens.

Roast for 2½ to 3 hours, until a leg easily wiggles out of its socket and the potatoes are tender. Tilt the chickens to pour juices into the pan, then transfer to a cutting board to rest for 15 to 30 minutes.

Transfer the potatoes to a serving bowl. Pour the pan juices into a measuring cup and spoon off the fat. Carve the chicken, stir the chives into the pan juices, and serve the chicken and potatoes with the sauce.