@moantoniaa The tunnels are connected with each other so if you use the correct option, you might end up with another exit than the one you came in with. Other than that, it's mostly exploring
Greg is usually easiest to find on full moon. He should almost always be at his hut during that time.
Do you not have the option to battle ?
Please move your mods folder to the desktop anyways and test without mods/cc. Also delete the localthumbcache.
EDIT: For the door. Does your Sim not go though if you just click somewhere inside the bunker ?