BRRRRing a multifamily property - dealing with existing tenants

My partner and I have completed BRRRR's several times - almost a dozen now. However, every time it was a completely vacant single family house or 2-3 unit building. We are working on getting a 2 unit (1 unit vacant) and 4 unit (no units vacant) under contract. We want to BRRRR the properties. All the occupied units are distressed/outdated and rents are severely under market. They are paying $450 and the market is $550 in current condition, and after being renovated they should rent for $700.

I should also mention literally ALL of the tenants do NOT have leases!

Can people please share strategies for this situation? Especially considering the current eviction environment.  Have them sign leases on day 1? Maybe 3-6 month leases? 

How can we gracefully, professionally and respectfully get the existing tenants out so we can rehab the units?