If your partner followed the agreement to "nth degree" you probably don't have an argument, but it sounds like it might have been her decision to change the agreement without your written consent or even discussion.

Your feedback is appreciated:ARTICLE12-AMENDMENTSExcept as otherwise provided herein, new Bylaws may be adopted or these Bylaws may be amended or repealed by the vote of a Majority of the Members, or by the written consent of such Members.

That same day the offer was signed, another agent from the same office held an open house (without our explicit consent, post offer acceptance).

In this case, you are basically stepping ahead of the original lender, but without their consent. 

@Alex Fabiano, in most states you must be at least 18 years old to enter into a legally binding contract without parental consent.

It will matter that they negotiated without her consent or authorization.

My lease states The only person(s) living in the Leased Premises is/are: (the husband & wife)  A.Any change in the occupancy will require written consent of the Landlord and may be subject to an adjustment in the amount of rent. 

To NOT permit any guest or invites to reside in the Premises without prior written consent of Landlord.I think this is pretty clear that by allowing another person to move in they have breached the lease.

All in all, you need the owner's consent and cooperation.

The guy on the lease sleeps in the living room and rents out the other 2 bedrooms for $450/mo to other college students and I do not think he has consent of the landlord.