Goodday great people,

Please this question is for the structural engineers/builders here:

There are thin visible cracks (fault lines) appearing on the interior walls of a building i manage and it's giving some concern. The building is a 3 storey building and these cracks are occuring in one of the flats on the first floor.
Now i googled "cracks on walls" and got some info about the different types of cracks and how serious they are.
The ones that are visible are springing up
- close to sockets (step like cracks),
- close to the top of the door edge (horizontal)
- there is a vertical line at the edge of the wall (almost not visible)
- then there is this step like crack on a wall in the flat that's starting from the floor, ascending all the way to the ceiling.

Please my question is how can it be remedied. Cause from what i researched, i read it could structural. I also read that some of the cracks are not really serious, they only need to be scrapped and replastered then repainted.

Your candid professional advice will be highly appreciated. Thank you