You will want to consult with a lawyer.In regards to your last two questions here's some background on what makes a contract valid and enforceable:Offer: A promise to do or not do something within a certain time period Acceptance: A clear and direct statement that all terms and responsibilities are accepted Consideration: A legal and adequate inducement given in exchange for the promise Capacity: The parties to the contract must have the legal capacity and competency to contract Awareness: A party must be aware of the contract Legality: The contract must be legal in the jurisdiction it will be operating in***Not legal advice*** Steps I would take: -Review contract in detail to understand each counterparties responsibilities (if you are not aware)- Email a copy of the lease to each of the tenants listed on the lease and reiterate lease expectations for termination notice, rent payment etc. - If the lease was signed via Docusign (other esign may have same ability) - you can go to the envelope, go to history and view the IP addresses for each action taken.

One said the 2nd mortgage has to be assumable and the other said it did not.VA issued Circular #26­24­17 back in August to try and clear up the issue:Assumability: If the secondary borrowing is not assumable, the holder of the VA guaranteed loan should counsel the assumer that this may restrict their ability to sell the property to another creditworthy assumer through an assumption in the future.The lender currently servicing the loan still can decide whether or not they'll allow the 2nd.You could do seller financing for the gap and then refinance just that amount with a Home Equity Loan or Line of Credit at some point down the road. 

Quote from @Daniel Hale: Steer clear.  

During the partnership, you can jointly manage the property, increase its value, negotiate a flexible repayment plan with the seller that allows for larger payments after the property appreciates, ensure a written agreement that clearly specifies repayment terms and timeframes and refinance, and the sellers are able to 1031 at their leisure? 

Sounds like it makes sense for you to partner, I would suggest: spell out responsibilities very clearly, how you make decisions and most importantly: have a very clearly spelled out exit. 

Building trust can lead to better negotiations and more opportunities in the long run.Managing seller relationships is about clear communication.

The biggest lesson, which I learned early on: get clear on the type of property you want to buy, then tell everyone over and over again.

A lot of people (myself included) use multiple baselane accounts and sub-accounts to keep things as clear as possible relative to each property.

There is a problem, but they always need somewhere to go and will never sell until that is clear and the path is set.

Signing at closing, it's a short-term lease, sec deposit is a full month's rent, and there is a clearly defined move-out date.