To answer one of your questions regarding putting the brother on the lease as a tenant and not a co-signer - if you did that, then he would be a tenant, and he could move in.  

We pretty much got everything we wanted in a tenant.At minimum get them to provide a co-signer with STELLAR credit.  

It's time for them to have a chance, but only with a co-signer.  2009 through 2012 was a bad market for Real Estate.  

Tenant 2 found a co-signer who will be moving in so now I have on my hands one tenant removal, one co-signing party and a co-tenant signing onto the lease.

And a large part of investment management is understanding and minimizing risks associated with your investments.If you're not quite sure about a particular tenant, to address your risk you can (1) ask for a higher security deposit, (2) offer a month to month lease, and later be willing to convert to a longer 12 month lease if both landlord and tenant agree (makes it easier to evict in month-to-month lease if necessary), and/or (3) (if income or credit is the issue) ask for a co-signor. 

A co-worker as a roomie could get ugly too.

But, hey, the co-signer probably paid their rent every month just to be sure they didn't move back home LOL.If you take a co-signer, be sure they're also only on a month-to-month agreement, so you can kick them out for all and any other reasons.  

The mom's credit score is almost 700, and she talks very sincerely and looks eager to move in.3.A group of 4 college senior female students and a co-signer who is the father of one tenant. 

Learned that the hard way.Plus, a co-signer does not guarantee good behavior.  

In this case, when you sign the lease, does the mother is part of the lease or does she become a co-signer.