New Lease Contracts @closing?????

[Nathan Henderson]

I have 6 units currently and the purchasing and closing on those properties were relatively eventless, very smooth. However, I am in the final stages of closing on a quad that is 100%. Three tenants have an existing lease with the current owner @ $750 a month which covers rent, water, electric and trash/sewer. The fourth tenant doesn't have any lease contract due to a family favor/living there and paying $750 rent under the table because they know the owner. I am not going to pay for utilities!! So the option I am going to give them is to drop the rent to $650 but with no utilities. My intention is to sit down and professionally and politely inform them of all changes coming due to transfer and that I value them as a tenant but we are going to have to work through a few growing pains. So what are my legal recourses if they don't sign a new lease and won't move? Do you need a lease contract to serve eviction? Or would it be criminal trespassing at that point??