Tenants paying WAAAYYY under market rents (Legal)

[Paul Wakim]

Hey everyone, 

So I have a strong lead on some properties in the East End of Pittsburgh, one of which is a 4 plex that is more like townhomes from the 40s. 3 are rented, 1 is vacant. The rents are.... wait for it.... $370/m, $550/m, and $555/m. In my opinion, the rents could very easily be $1000/m or more with minimal work.  I have the opportunity to purchase this property off the market and I am really worried about the laws of raising rents or evicting tenants. Unfortunately, these tenants are elderly and have been living in these units for 25+ years so it's going to be hard no matter what to make this decision. 

Has anyone heard of or dealt with a similar problem first hand in PA or better Pittsburgh? 

What are the laws around purchasing a new property and immediately raising the rents or evicting tenants with the goal of getting higher rents? 

Thank you in advance for your help!