Cash for keys in Chicago - Best procedure?

[Edouard Pierre]

Hi! I'm in Chicago and in the process of closing my first property where I'm inheriting tenants that haven't paid in a while. The situation: 7-unit building where the top two units are family and are both not paying rent. From what I have gathered from the property management (very poorly run since they're still residing in the unit) the tenants aren't paying because the property was in probate. Doesn't seem like it makes any sense because the other units are paying on time. 

My first thought is to do cash-for-keys but what are some of your experiences with the overall approach, amount, and successes/failures? The last thing I'd like to do is waste money, months of lost rent, and time by evicting these tenants. 

Once I close on the property do I serve them a 5-day notice? Do I then serve them the document I have had drafted by my attorney regarding the sum I'd offer, date that they need to vacate, and overall agreement that they don't trash the place?

Is there a rule of thumb for the amount that a landlord should offer the tenant (1month, 2months, etc?)?

Lastly...these two units are occupied by family members. They share the same last name so I assume they're siblings but I don't know anything else. Could this be seen as an advantage? Could I just offer one sum of money which would equal less than if I offered two individual units or should I just stick to separate but equal offers for each unit? What a dilemma...I understand there's no one answer for this but any advice/experience shared would be greatly appreciated! 

I'm a real estate broker in Chicago who deals with residential, commercial, and investments. If anyone needs any help with anything, referrals for any service, or anything at all I'm at your service! Thank you again you wonderful BP-ers!