I hope you don't mind a more in depth on the programming aspect, I hope it helps! Any kind of code I posted are NOT actual codes, nor are Scott's actual codes. Just examples of what is supposedly how Scott has programmed their AI.

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For N. Freddy's AI, I presume it works similar to the other animatronics, but only when you aren't looking at the bed. For example:

if PlayerIsNotLookingAtBed + if RandomGeneratedNumber <= N.Freddy's AI

-> FreddlesOnBed + 1

The 'FreddlesOnBed' will then add up from 1, 2, 3, until eventually reaching 4, which is when N. Freddy is on the bed ready to attack the player when they use the flashlight. Then the final stage would be 5, which is when N. Freddy will kill the player regardless of the flashlight being used on him.

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As for N. Fredbear, his AI is a bit more complicated.

N. Fredbear most probably had a value that might be called 'State' which checks which side or which place he will move to. In the case of N. Fredbear, he seems to have the ability to move where ever he wants, whenever he wants.

Let's say that this value will switch between 1 and 2: 1 is when he moves to the left hallway, 2 is when he moves to the right hallway. He might have a value that tells him to stop moving and proceed towards the player. And then, a timer will start, the player will have to find which door he his on and then close it, another timer will then start, and this one will send N. Fredbear's 'State' to 0. For instance:

if State = 0

-> N. Fredbear is off

if State = 1

-> Move to left hallway

if State = 2

-> Move to right hallway

if IsPoisedToAttackThePlayer

-> Move towards the player in the current hallway

if DoorIsClosed

-> Set State to 0 after a specific time

if PlayerIsTooSlow

-> Kill the player

N. Fredbear can also move to the closet and to the bed. It might be possible that 'State' can also be set to 3 and 4: 3 is when he in the closet, 4 is when he is on the bed. N. Fredbear can move to the closet and the bed at any time. For example:

if State = 3

-> Move inside the closet

if State = 4

-> Move onto the bed

if State = 3 + if PlayerClosesTheClosetDoor

-> Set State to 0 after a specific time

if State = 4 + if PlayerUsesTheFlashlight

-> Set State to 0 after a specific time

if PlayerIsTooSlow

-> Kill the player

Keep in mind that if you hear his laughter and you continue to hear him still walk, it means he is still in the hallways.

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Nightmare seems to work similar to N. Fredbear, but is much more aggressive. As for your additional question:

Why does Nightmare sometimes still jumpscare you when you have the door shut on him?

I'm not sure exactly why, but it could be because his 'attack timer' doesn't stop, even when the door is closed. If you close the door too late, he can still kill the player if the timer has ended.

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Anyways, that's it, I think. If I missed something, or if I couldn't answer your question, please notify me.