Once you get the red (or blue) key. you must unlock the attic and grab the lock. If you have the blue key, unlock the shed and grab that lock.

Wait for the guest to enter his bedroom. (The code-locked door)
Left click or press the USE key to put the lock on the door.
You now have the whole house to yourself!
Simply use the key on the lock to unlock the door.

Get the yellow key.
Put it somewhere safe. Like in your van.
The guest keeps trying to get the key, but he can't go inside the van, making him stuck.
The guest will chase after you endlessly if you have the key in hand. Also he can sometimes grab it through walls.
The guest can also still see you in his house sometimes.

I'll add more ways to trap him when I find more.