Am I living in a potential tri-plex house hack?

[Blair Lee]

I think I am living in a House Hacking opportunity but not sure.  

We live in a duplex (in-laws on the other side) which used to be used as a tri-plex.  My family got bigger so we adopted the smaller 3rd part. 

It is in desperate need of a new roof, so my in-laws (who just sold their house to move in) wanted to just pay for a new one for 30,000 €  (we live in Hamburg, Germany).

But what if we combined our capital for a down payment on a loan and rehabbed this house into a fully functioning modern triplex.  Then rented out the 3rd living space? 

- We could share our big yard. 

- They would have a place to park. 

- We are almost central to the city with good transport system.

- good schools in the area

What would you do?