Eviction is a very specific process that must be followed to a tee. Do not try and wing it or you may be spinning your wheels. Consult a local attorney or possibly a very experienced agent to get the precise process for Ill and Cook County and follow it.
If you were my client I would include in the contract that the home is to be vacant prior to closing and subject to re-inspection for any damage done by current tenants. Any repairs are the responsibility of the seller at the seller's expense.
As closing date approaches, drive by the home to see if there are signs of packing. If the tenant shows no signs or interest in moving on, don't close.
The landlord Tenant Act in Florida will spell out the rules and obligations for everyone involved. Chances are if the tenant will require eviction activity to move on, you don't want to be part of it. Put this on the seller if at all possible, it's your best bet.
1. Consider placing goats, chickens, dogs and cats in both the front and rear yard. Don't forget the fence. All the above animals are legally allowed to be outside, on private property, in Chicago. Even in winter. Then advertise free fresh fecal matter composting classes. It might not hurt to post a large sign outside the gatherings that states, "Please do not disturb tenants. They refuse to pay rent or vacate the home. Please honk to show them your support."
2. Start a twitter feed. Call it Squatters@1234StateSt (or whatever you address is). Post a series of twits saying things like, "With the rent I saved this week, I bought two blow up dolls and an IPAD#squatter1234state", or "I squat because it is human. Do not pay others for their work. Ok I am an idiot.#idiotsquatter1234state". Keep it going. Get the newspapers and other social media to help it go viral. And don't forget the jumbotron screen you will put in front of your property, posting all of your 'tenant's' tweets, live.
3. Buy a van, a large dog catching net, and a couple of big sturdy canvas bags. You'll figure the rest out.
Now that you've filled in a bit more, it's more complicated. Family, or ex family does what they want, when they want. I don't really have any other advice except if they don't show signs of leaving and you close, you'll be paying for the eviction yourself. If it were me, I'd pay sooner rather than later if you have any plans on moving in or getting other tenants. Just don't give the money to anyone that you're related to. Pay the people involved in doing the eviction directly and stay away.