Yes, he can be sued by the seller; anyone can sue for almost any real or imagined cause.  

You can also hire a real estate attorney off of UpWork or Fiverr to review the documents and give you an opinion just to be sure.

Also, if your wife and her parents were the real estate investors first, why aren't they weighing in? 

Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

And it can work really well for you as long as you pay attention to the statute requirements.In order to defer all tax you are selling investment real estate and buying investment real estate of at least the same value you sold. 

2) How many hours/week do you really want to commit to for real estate?

Find a great real estate attorney to help you with:1) Putting a lien on the property, with your aunt's consent, to cover any work you do.- Ask the attorney if your aunt & dad need to authorize lien, or just aunt.2) Understanding your options to force payoff of the lien.- Ask attorney how you can enforce collecting on the lien when you need to.3) Getting full control of the property, while allowing your aunt to keep her ownership.- Have attorney draw up a contract to do this.Suggest you offer your dad some cash, now or in the near future, to motivate him to transfer his ownership to you.It may not work out, but you will learn a lot either way!

@Nicholas Stout Normally when I hear landlords make the conscientious decision to "convert" their properties to Section 8 rentals, they have a real estate problem wrongly diagnosed as property management or tenant issues.

Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

Feel free to DM me if you'd like more insights on all this (we don't do biz in Alabama so got nothing to lose).Here's some other "copy & paste" advice on how to search for a better PMC:----------------------------------------------------------------------------------------------Recommend exploring as many sources as possible to get referrals AND cross-reference them to get as much accurate information as possible.Check out NARPM.com, BP’s Property Manager Finder (BiggerPockets: The Real Estate Investing Social Network), etc.Also, encourage you to learn from the mistakes of others - by reading posts here on BiggerPockets about owners not having their expectations met by their current Property Management Company.