Here are few:No need for a custodian (save $$ on transaction and asset based fees)Checkbook control - you don't need to ask custodian consent to make the investment, simply write the checkRoth sub-account - in essence you can have two accounts in one: regular pre-tax as well as Roth after taxHigh contribution limits up to $56,500 per year, this is nearly 10 times more than an IRA.

Lease LanguageMy lease states the following related to the subject: No more than 3 persons may reside on the Premises, unless the prior written consent of the Landlord is obtained.

If so, by what authority can they interfere with a legal contract between two consenting parties?

If all or any part of the Property or any Interest in property is sold or transferred (or if Borrower is not a natural person and a beneficial interest in Borrower is sold or transferred) without Lender's prior written consent, Lender may require immediate payment in full of all sums secured by this Security Instrument.

If they don't have the funds, then they HAVE to reassign the property WITH my consent. 

Since the option to call a note is at the discretion of the lender, there is no statute of limitation.Chris is correct that permission may be granted, rarely will it be in writing, implied consent is common, that is not actual consent as described in a standard deed of trust.

I just completed inspection contingencies for the property I am in the process of buying, and to my surprise, my real estate agent emailed me to consent to a dual agency contract.After doing a quick Google search, I discovered that this should have been disclosed from the get-go.

She's even replaced their kitchen's double oven with a better double oven without consent which she is currently paying the replacement costs. 

Does the living owner have sole rights to sell or do the children need to consent on selling? 

First, communicate your plan to the mortgage holder, securing written consent and checking the mortgage agreement for any restrictions.