death masks

On one of the second floor balconies, you'll be attacked by dogs. After you kill them all, check one. Its collar has a tag on it. CHECK the tag. It expands into a False Key. Go to the room with the Shield Key on the floor. TAKE the Key and immediately USE the False Key to keep from being killed.

I can't help you with ALL four masks, only 1 of them. But to get the shield key, go to the study after you get the sword key. To get to the study, just go into the main hall, find the only door on the second floor that takes the sword key. Go in the door and follow the hallway, no zombies are in the hallway. The study is at the very back of the hall and it is unlocked. Turn to the right inside the study and get the dog whistle. Next, go to the second floor of the dining room and go to the second door on the right side of the room. If you're playing as Jill, you'll use the lockpick to open a steel door that leads you outside. If you're Chris, you need an old key. Go outside and follow the walkway. Blow the dog whistle and you'll be attacked by 2 dogs. Kill them and take the collar from one of them. Examine the collar and a tag will fall out. Examine the tag and check it, it will turn into a false key. If you've seen the real key, then go to it, take the key, put the false key in the socket, and there you go. You now have the shield key.