這點事情都解決不了，業務水平需要提高。

Be considerate.  He got sick leave and had plenty of time on his hand, so he was just being restless.  Just say no, thank you, good luck.  Have thick skin. 

 landlord is only in charge of Habitability, i.e. plumbing, electricity, appliances, doors and windows, etc.  Whatever the creek or trees is not your problem.

No need to ask them to leave.  

If you can't deal with this minor issue, you need to raise your game.