Fixing the cracks
Being a landlord doesn’t necessarily mean that you have epic DIY or building skills. You might not know how to replumb a shower, or plaster a wall. That’s fair enough, but in these cases, it is usually a good idea to have a number of people who can do these things for you.
It’s not a good idea to jump in with both feet if you don’t have the slightest clue what you’re doing. Otherwise, you’ll end up thinking that nailing a plank to a ceiling to hold up a crack is a perfectly reasonable fix for the situation. Which will just result in a larger building project in a few weeks.