This is the link you need to click to look at the google files.
These graphs are just for visual representation so you don't have to read the notes at a first glance. Enjoy! 
TLDR | Pictograms, Legends, and Notes. Legend:
White = 1st Player's line of sight and their training rotation.
Blue = 2nd Player's line of sight and their training rotation.
Orange = 3rd Player’s line of sight and their training rotation.
Green = 4th Player’s line of sight and their training rotation.
Notes:
So it's a little hard to see in the diagram that I've chosen, but the 1st player needs to stand next to the first barrier that everyone sees when the game starts and run around the columns with the weapons that suit your play-style. The game gets challenging as you avoid the HELP door and take the stairs up and then down to the Mystery Box. The HELP door should completely separate the group in half by using the floors and rooms as funnels. The 1st and 2nd players get one half of the bunker on each floor, so do the 3rd and 4th players. Each player sort of reduces the work load, starting from the basement, then up the stairs, through the balconies, and down the stairs again into the lobby.
It's possible for the 2nd player to defend the upstairs and train around their balcony by themselves. They need to be skilled enough to train within tight corners and should not get stuck against the middle column, which is really difficult to do consecutively. This applies to every other player as well. Each room will possess its own challenges and rewards. A good rule of thumb to have in your lobby would be to note that everyone needs to avoid falling back into the 3rd player's territory (located on the second floor) as much as possible. This is what I will consider fallback territory and that area is located between the BAR wall-buy and down-stairs to the Mystery Box room. This pathway needs to be more clear and rather than congested like a Verruckt hallway.
Everyone will have to stay in their own sections as much as possible by saving a crawler. This should give everyone enough time to hit the box by the end of a round, consistently. There will be territories good for farming power-ups, located on the first floor. There are also congested areas that everyone should avoid for more freedom to train in space. These territories will have to be negotiated over chat, when possible. The HELP door obviously needs to be closed on the first floor, and should not be opened once the stairs to the second floor have already been opened. The HELP door is kind of a last resort to save yourself or to save the HOST in the first room if everyone is down for the count.
This strategy was implemented by myself, and a couple of friends, so it is possible for a full lobby to perform if well-coordinated and can be performed as low as a trio group. I would refer to John_Banana's previous stream provided below for a visual example. It sort of happened.
Link:
Call of Duty: WaW Zombies (NEW UPDATE for remastered mod)