Any way to guarentee tenants move out and don't need eviction

[Ben S.]

I have 8 units with tenants in a property I just purchased. The property needs significant rehab, so I need everyone to move out (both to start work asap, and so someone in the county doesn't decide to get upset that people are living there with probable health violations and such). I legally only need to give 30 days notice, but as some of them have lived there a long time, the sargent and eviction officer I spoke with recommended I give 60 days notice to ensure any eviction process goes smoothly. I was okay with that since I can't really start the rehab that soon anyway. 60 days notice means 90 days total if I need to evict.

Now I just had one of the tenants call me and ask if I could give them 90 days so their kids can finish school before they have to move. 7 of the 8 units have kids (some have a lot). I was expecting 90 days anyway, but if I have to evict after 90 days I may have a total of 120 days, which I'd rather not have. Is there any way I can help guarentee everyone will move out by day 90?

I though about requiring that they show me a lease or proof that they have a place to move to on day 90 (requiring it by day 60 or I start eviction then), or some kind of fine if they don't move out by day 90 (though I don't think any of them have money so suing if they don't pay wouldn't get me anything). No one has a lease (I assume they all did at some point with the previous owner, but some could be squatters for all I know).