I have told her that they would need to reach some sort of formal agreement, that I cannot take her off the lease without his consent.

The TCPA requires that a business must receive express written or opt-in consent from any contact before it can legally start sending them SMS marketing messages.

We reached a consent judgement, but it the end of the 40 days she asked for extra time.

I don’t know about the US, but according to German law you would not be able to purchase her share without consent of the other heirs.

You won't be able to take him off without his consent. 

Aware that the consent of lender will likely be needed and that loan documents should be reviewed to for due on sale or prohibition on transfer provisions. 

I plan to let them keep the cameras but will issue a warning, as well as will have them sign an addendum protecting myself from potential liability related to audio/video recording without visitors' consent, or privacy intrusion liability if the cameras are capturing parts of the neighbors' properties.

Custom forms could easily prohibit assignment without consent.

The seller already signed consent of dual agency months ago when they listed the house. 

https://www.rentspree.com/blog...Landlords and property managers are approved by FCRA regulations to legally review a tenant’s credit report (with consent) for the sole intention of determining an applicant’s qualification to rent.