Tenants in a 4 unit multifamily, what are our options?

[Jorge Leon]

Hi all.

My parents are looking to purchase a 4 unit near their primary residence. 3 of the units are rented and one is vacant. The tenants have the right to stay until their lease ends correct? At which point rent would negotiable if they want to renew? The reason I am asking is because the units seem to need some work, and although we are not in an immediate hurry, we would need them vacant for that, we're just looking at our options. 

Also, it is my understanding that rent being currently paid can be used to calculate whether their DTI qualifies, is this correct? Can we ask the listing agent for information regarding how much they are paying? Would they provide payment history for use in loan qualification? Any advice would be appreciated.