Note: This map is from Mission M00 of PO. In this case the door is still closed
Question 1: Does the zombies still splits when coming from the Spawn Point?
Question 2: In this case does some of the zombie stay and the others split if the zombie are coming from the Black Circle?
PS: The zombies here doesnt see any players on site. And as far as I know zombie goes to the near loudest noise even if there is something blocking them.
1 - No they don't. There is only one path to the noisiest zone until the door opens. Once the door opens, then they will start to split.
2 - Again, no. Only if there is no clear path do you ignore closed doors that are blocking zombies.
If there is an open path, you do not count paths that go through closed doors. If there are no open paths, the zombies will take the shortest route, ignoring doors, but again this is only if there are no open paths. In both of your examples there is a clear path, so the zombies don't consider a route going through a closed door.