Yo! Looking at a 4plex with m/m tenants below mv, advice?

[Reggie Maggard]

Im thinking about pulling the trigger on this 4-plex with renters paying 550 and 600/m. Market rent seems to be 700-725 for comparable units. If I buy the property, how do I nicely tell the tenants I need more cash now? It doesn't help that one tenant is a little old lady. 3 units are m/m and 1 unit just signed a lease for 24m at 600/m. Also, none of the tenants have deposits.

Much apprech for the advice guys!