By whom?
And why?
The owner has a reason for unloading the property on you for free.
You have the option of declining the gift until the upstairs tenancy is resolved.
Once you own it you could end up spending umpteen thousands on getting them out and addressing the mess they leave behind.
Yes, worry. At least one consequence has already been revealed in a previous response.
So, you've been warned. Heed it.

