Purchasing property with no lease agreements

[Pete Harper]

I’m looking at a distressed property that has four of six units occupied. Two units are paying only $400/month for 3 bedroom, 1 bath. The other two are not paying anything. The seller is very eccentric to put it kindly. In negotiations he says he has no lease agreements with any of his tenants, not willing to provide any records or other documents.

How would you handle this situation? I’m likely to need to evict the non paying tenants straight away. I’ll try cash for keys first then go to court if needed. This is in Landlord friendly Texas so I’m not too concerned with evictions. The other two paying tenants are $300 under market rent even taking into consideration the condition of property. I usually try to honor existing lease agreements but in this case there is nothing in writing. Do I give the paying tenants 30 day notice of rent change to market rent? The remaining two units I plan to fix up and rent at market rent.

Any recommendations?

[Pete Harper]

@Ujwal Velagapudi The Seller is not so devious. Just an eccentric old man who has gotten in over his head. Squatters are most likely old tenants who just stopped paying. 
@Evan Polaski I do not think the seller is capable of getting the old tenants out. If he was able to evict he would have done so already. I failed to mention he is in bankruptcy. He owns a bunch of properties and is selling stuff off to pay creditors. I’m getting rock bottom price so I’ve factored in carrying costs. The two vacant units look rentable and will carry the mortgage while I get the other four ready. 
My main concern is he-said, she-said arguments should I have to drag tenants to court.