"Valid housing" - does this work?

Solution 1:

Assuming that all of those have walls and a light source, those would count as valid housing. The requirement is that it has a door, not that the door go anywhere. Also notable is that wooden platforms count as doors for the housing rule, so you can actually just have a wooden platform separate the rooms from each other as well.

Here is an example of housing with internal doors:

If I can, then I'm going to be making pressure-plate/activator automatic doors that don't get torn down in a blood moon.

This is actually a very common strategy to defend from a blood moon. As noted in the Base Defense Guide on the Wiki:

By using actuators and Grey, Brown, Blue or Lihzahrd pressure plates, you can create a player only door that doesn't even require you to use your mouse. Setup the door as you would an active stone/actuator door and because Grey, Brown, Blue or Lihzahrd pressure plates can only be activated by the player no mobs are able to enter (nor escape).

You can also just place a torch or other item in front of the door so that it can only be opened when you are facing towards the outside. From the wiki:

Another way to prevent enemies breaking down your door is to place a non-solid object, such as a chest, wooden platform or other Furniture item, on the inside of the door. This will prevent enemies from opening it but will require the player to face away from the house to open the door.

Solution 2:

The structure does not have to be "accessible" with a door; as in you can create a switched active block entry way so that Blood Moon/Eclipse mobs can't get in. You can also create a double door entry way, where the outer door is the switched active blocks.

Another way, would be to place a platform, container or decoration against the door. This creates an "open from the inside only" door, that can't be opened inwards (the direction most mobs are headed to get inside your house). The exception to this is goblin armies, as they break the door instead of opening it. The "issue" is that YOU also can not open the door inwardly. You would have to face out and click to open the door.

In your diagram, the C/D version where there is a switched "ceiling" between the doors is a good way to do it.

Solution 3:

I would say these are all valid if the requirements fit.

But you need to remember that the need to teleport into there houses wich means that you have to leave the place.

Second you need to think about monsters spawning in your house eg. Goblin Army.

third how will you talk with those npcs ?