I would only amend the lease by adding the daughter as an occupant responsible for payment and all other terms in the least.

Thus they can spread out their tax payments and not keep filing amended returns to recapture possible overpayment of taxes. 

You will either need to amend a prior year's tax return or file for a Change of Accounting Method (Form 3115).

If it doesn't autorenew, a simple one page amendment, referancing the origional lease parties, address, and ratificaiton date and noting the new terms will suffice.  

Is there some reason why I should do more than send an email to that effect; for example, is there some reason why I should present this offer as an amendment to the lease?

You need to review each lease to make sure they either conform to and work with your development plan, see if you can amend leases that don't work with your plan, or alter your plan to work with the current leases.I see an opportunity to create value in either event (that is under the current zoning/density or increasing density).

Based upon this change you would either 1) like to break the lease...you will continue paying rent until you find a new place, and will provide notice of your final date as soon as you find a place 2) you would like to discuss a lease amendment to reflect impact to the property you rented and the change in its condition.

Just received the amendment to address concerns after our 3 way call and it had two additional items that we didn’t discuss on the call so i wanted to push back and my agent asked if I wanted to hop on a call with the buyer’s agent.

if for some reason you get into a situation that a contract isn't assignable, you can always draft an amendment stating the contract is assignable and if both parties sign, you're all set!

I’m selling my home and we are past the due diligence phase and my handyman has fixed the items we agreed to fix as part of the amendment to address concerns.