It's heavily dependent on the types of properties and the effectiveness your processes and systems.If you don't have systems and processes in place, you may struggle to manage 30 on your own.

There's some mis-information and mis-understanding of AP, the process and it's effect in this thread.

Direct communication with the builder has been the most effective method in my experience.

New year, new laws (Senate bills 205, 206 & 207).Effective January 2, 2025, Michigan landlords can no longer consider a tenant's source of income when screening them. 

By recognizing the signs and implementing effective preventative measures, landlords and property managers can protect themselves from potential scams.

Alternatively, in addition to the per diem in § 17 (Possession) for failure of Seller to timely deliver possession of the Property after Closing occurs, Buyer may elect to treat this Contract as being in full force and effect and Buyer has the right to specific performance or damages, or both.22.

Are there any cost-effective ways to handle this situation legally?

They don't understand how to price effectively, study the market, set boundaries with tenants, establish policies and procedures, communicate, and dozens of other things.

Sub2 is a risky strategy for a long term buy and hold as the longer the deal structure stays in place, the higher the chance that issues will arise (like issues with the loan servicer, insurance, seller filing for bankruptcy, seller dying, seller realizing their DTI ratio and ability to buy their next property is negatively effected and becoming upset about it like in your case, due on sale clause being called, etc.).

@Hamidou Keita I would recommend if duplexes are limited if you can get a 4-5 bedroom house and either rent by room for house hack or splitting a big house into 2 and adding a kitchenette and separate entrance as a more cost effective ROI option