You can post a reminder about quiet enjoyment of the property as per the lease and say that you received a complaint-no need to say from who as it could have been any of the neighbours.

This is something that the tenant and neighbour need to work out, the same as they would if they were both owners which is what you said. 

If I got complaints from the neighbours, I dealt with it quickly and evicted the perpetrators.

I know my own area very well, but unfortunately $700k is the low end for this and neighbouring counties and I don't know anyone buying for that amount.

I am building's owner and I will appreciate if someone has any advice about how can I find trusted real estate agencies or real estate investment companies which probably they will have interest in Athens, Greece.

She made out well being able to do airBNB prior to you buying it and getting $5K from the previous owner to move out of the main house.She's going to be your neighbour and tenant for 18 months, just leave it alone and when it comes to renewing the lease, if she's otherwise good, bump it to slightly more than market value (this will get you some of the money back) and renew it, if she's difficult...don't renew it. 

Risk aside, they're otherwise quite profitable as Airbnb's.Never heard of an executive rental but from what I've just read, it sounds like you'd be able to circumvent the possibilities of pissing off all of your neighbours while still getting the benefits of higher rates from STR.

Property and financing details:A neighbour in this complex passed so my brother, and I are considering purchasing it as our first investment property.  

, meaning i can't just go and ask the neighbours physically.  

@Chris WaltersYou will have to canvass the neighbourhoods, speak with tenants and neighbours, and/or establish a subscription to the Land Registry (if you will be conducting lots of queries, it may be worth while).