You'll need an authorization in writing from the owner to speak to the bank about their account. 

This part of the island is probably the most diverse region (based on property types and features) and the largest geographically. 

It's intelligent to follow the law and let the authorities deal with this situation properly.You don't know how violent this person can be, and ending up a statistic does no one any good.https://nypost.com/2014/01/05/slain-slumlord-found-in-trash-had-enemies-list-a-mile-long/

After that it's up to your local H/A (housing authority) to figure how much they want to pay.Ask your voucher person and his caseworker what they can afford. 

Yes, that process exists, but you're at the mercy of the local housing authority and how they want to spend their HUD funds. 

I am planning to buy a property that I have been managing for several years. then I just found out that there is an illegal renovation that happened a few years back without the city authorization.

Needless to say, rezones are not something that jurisdictions take lightly because they are responding to the jurisdictional authorities (city councils and mayors offices) as well as the surrounding community, which is why it takes so long.

You can always walk away if it blows the numbers, or re-negotiate with the seller.Taxes are one of the largest expenses for rent properties so should always be part of due diligence. 

This management company would own absolutely nothing, but it would be authorized by the main LLC to lease out the property.

You can contact the local housing authority to see if the voucher can be used as any leverage, but you need to keep in mind that a.) you will likely never collect the money if she moves out, b.) your prime goal is to get the tenant back on track or to get possession of the property back and minimize your losses.