Keep totally separate accounts, merge everything, or make a stand-alone new joint account? 

Can we simply add him onto my account as joint holder in order for him to have proof of funds to close A.S.A.P and not run the risk of loosing the property?

So, in this case, would having the son added on the lease give the dad the same flexibility to break the lease when the deployment happens because the lease is jointly in their names?

There are some inferior operators out there. 

You might want to do a Joint Venture with someone that provides the financing.

If coming up with the down payment is an issue, you could find a joint venture partner - someone who has the cash and is willing to partner with you on the project.

Ray Kroc built a whole empire out of realizing he could sell cheap crappy hamburgers as long as the johns in his hamburger joints were cleaner than the next guy's.

"jointly and severally liable".

I'm looking to connect with other investors to do joint deals. 

More of a joint venture I guess to obtain the home with other peoples money and then fixing up and managing the properties myself once the ARV is higher and I can cash out the people who put the money in.