You can get "Go Towards the Light" and "Ahead of the Game" at the same time.
When playing as Chris, advance until you have the real Armor Key. Collect one of the Small Keys in the mansion and continue until you are in the Save Room where the Serum can be found.
Exit that save room and continue down the hall. You will find two doors near each other. The door to the F-shaped corridor can be unlocked with the Armor Key and the door next to it can be unlocked with the Small Key. Enter the Small Key door first and collect a flash grenade in the room. Then return to the previous hall and grab the second flash grenade in the F-shaped corridor.
Now you have all supplies, you can do this anywhere but I found it easiest to continue to the plant in the nearby room and use the Chemical to kill it. Then leave the room and run through the F-shaped corridor (without killing the two zombies that bust in from the windows) and return to the nearby save room (where you find the serum). Equip a pistol (any gun likely works) and make sure to equip the flash grenades as your Defensive Item then save the game.
Now simply exit the save room and return to the F-shaped corridor. One zombie will be standing in front of you and the other down the hall to your right (not facing you). Allow each zombie to grab you and use the flash grenade defensive move. Right after Chris shoves the grenade in the zombies mouth, aim and fire. It will count both as a flash grenade kill AND a headshot kill. Then Quit and reload your save to repeat. Much less time consuming then attempting to grind the two kill types separately.