My question is: Since the contract is under addendum; can I market the house to potential buyers on my website and social media in case the first deal falls thru?

There is nothing wrong with that model, it's a win-win for both as long as both sides have integrity, the proper expertise, and the active partner is treating the JV's funds with utmost care.  

Investability - https://www.investability.com/ - As a vertically integrated solutions provider to the SFR investment sector, Investability Solutions is able to assist investors throughout the investment lifecycle.MISC.

https://www.cbsnews.com/media/americas-top-10-tech-cities-arent-on-the-coasts/4/Phoenix - #3 Market for Tech Job GrowthOne-year tech job growth: 188 percentMedian early career pay: $58,400Median midcareer pay: $96,800I'm friends with the CEO of a major start-up firm out here and all he talks about is the tech growth in downtown Phoenix.

Which social media platforms did you use and which targets did you set for you demographics. 

Social media will get you a zillion calls from wholesalers, claiming to have a huge buyers list (some actually do) and therefore the ability to close.  

I have a couple friends who invest in real estate who highly recommend a West Van company that integrates the legal and accounting stuff to make it simple.

You got to have all your social media covered. 

Using handwritten solicitation letters might help you.Keeping up with people that give weekly webinars like Paperless Agents talk alot about real estate marketing and how important it is to have knowledge, using professional-looking pictures and video, and popular Social Media advertising. 

The property management software we use integrates with reliable screening for our background checks.