Email scraping & emailing the users from CL without their consent can be considered spam, & can have consequences.

If a realty agent has a problem submitting a low offer, he/she is worrying too much about the other party who are consenting adults under the law and can make their own decisions and research to decline, accept, or counter the offer.

The problem is in a multifamily unit the other renters can neither truly consent to second hand smoke exposure or avoid it entirely -- they're sort of captive in the situation.

He specifically states he gets the landlord's consent to do this. 

I want to send a notice introducing us as the new owners and giving them notice that in order to renew their lease they first must consent to a criminal, credit, and eviction screening under our new minimum qualifications/new lease terms for all persons over the age of 18 that live in the home and also inform them that rent will be increasing November giving them the chance to stay if they want  and meet our rental qualifications or decide if it's best for them to move.I want to know does this seem reasonable and if there are some things I should consider before moving forward with this plan?

Valid, enforceable contracts cannot be unilaterally cancelled by one party without the consent of the others, unless there's a breach of the terms.In other words, your agent is under no obligation to cancel the listing contract, unless they either consent to it, or there are terms governing cancellation in the contract language itself - normally an expiration date of the contract.Another poster suggested that the contract may prohibit you from marketing the rental on your own.  

Did the brother consent to the sale or was it sold from underneath him?

Unless you recorded the conversation with the consent of the manager or its written in the lease I don't see that happening.

.- Your consent is needed to run your credit.

I have asked for the written consent ...