Messed situation. What you should do?

[Stelios Gerantidis]

Hello everyone, to introduce you I am Stelios from Greece - Heraklion and I try to complete a transaction on a 2 apartment (whole 3rd roof) building. These 2 apartments back in the past was stated as 1 house and in the mid of the house where the stairs appear to be today , it was the house's hall, as the years passed the old owners decided to break down the hall's wall and make it practical to be 2 split apartments but they didn't change the contracts to appear as it is now and also the architect didn't change the files of the house as well. After a long time, the new grand owner got this house that appears theoretically in files to be 1 house and but practically to be 2 split apartments. My architect got the files at the beginning and fixed the problem cause the seller said that he is not paying anything that needs a fix cause he sells in a big price discount ( 23600€ for both apts). We were at the point that my notary asked me to get the seller and the other floor's owners to sign the new contract that will show the apartments as they appear to be, but here comes the action. The seller was saying to me that the other owner is his uncle and he will sign when the time comes and that there is no problem. Well on my last phone he told me that there is no way that this uncle will sign the documents and that I had to say to him that it requires a sign from his uncle(which is a lie cause I've told that to him). I tried to find his uncle but he didn't even want to speak to us cause he had big property problems in the past with the sellers Father. My attorney which specializes in Real Estate says to me that in such cases if the other owners do not sign there is not anything that you can do and it's better to leave the case cause I will just waste my time and will have no results. Just to let you know my attorney said that pre-agreement contracts will not protect me against such cases according to the law in Greece.

Notes: 
-All the three roofs in this building have the same urban planning violation. Which means that if I decide to denounce they will be all in big trouble and will have to pay forfeit (this is the last and most not wanted scenario for me cause I don't want to mess more the situation, I'm trying to find a solution here).
-There are 2 owners and 3 floors plus the ground floor.
-My architecture engineer has locked the floor that I'm buying and she can do anything I ask her to do, which means that the owner right now don't own this part of the house If I don't let my architecture engineer give files and access, so practically he cannot sell the house legally right now cause it's like I locked his access to this part of his ownership. (I had to protect my transaction somehow and he signed for it).
-He doesn't pay the money I spend to my architecture engineer for this case

So what do you suggest for this case?
What would you do?