New Landlord with existing leases

[McKinsey Alston]

I am in the process of purchasing a duplex with an additional apartment on the property. Currently, the owner lives in the top unit and has the bottom unit of the duplex and the backyard apartment rented out. Both are on lease until 2021. Since I did not personally screen the tenants, what should Or can I ask the current owner about the tenants? Also, I have my niece and nephew that stay with us and want to ensure they’re safety. The property is in New Jersey. Any thoughts?