Evicting Tenants prior to or at purchase

[Jared Mink]

Hello! I'm wondering if anyone has had experience with a similar situation to mine and or has any advice.

I'm looking to buy a triplex as well as a single family home that is on one parcel, so 4 total units. All 4 units are rented but at half as much as market value. 2 of the 4 tenants have lived there for 20+ years and one of those tenants is a hoarder and their unit needs gutted. I would want to make improvements to all units and increase the rent to market value when the renovations are completed. There's no way I could keep a tenant in the unit while renovations are being done, and frankly the current tenants are not ones I'd be upset if they left. So here's the question, How can I legally evict a tenant who hasn't seemed to do anything wrong except created a landfill in their apartment. Is that reason enough to evict? I don't think I can ask the seller to evict prior to purchase, although that would be the best scenario. I don't know when their leases are up or if they're month to month. 

Thanks in advance for any suggestions!