A double closing means the property is technically changing ownership twice, one right after the other.

This concept is used to differentiated between a simple lease with an option (which doesn't shift any of the burdens and benefits of ownership) and an land contract sale (where the determination is that the sale has occurred even though the deed does not transfer until the last payment is made.You'll want to avoid that "risk of loss passing" threshold. 

My lawyer suggested tenant in common approach for this...as I will be giving him 25% of my 50% ownership for downpayment.

5 partners, all with active ownership can spell trouble.

This will depend on several factors such as your ownership percentage in the partnership and how active/passive you are.Another thing to consider is if it opens you up to filing in multiple states.

If its really good deal you should be able to BRRRR it and pull some equity out. in regard to ownership history, did you try the county and city records? 

Without my license I still get questions and help friends with real estate questions both for investment and home ownership.

Specifically, what amendments will need to be done to make the lease apply to my ownership and up-to-date with all legal requirements. 

Additionally, there's no lien placed on the home, they just record ownership of the panels.

This being the case I have put off a mortgage and was intent on saving over the course of 7 years towards the ownership of a home, at which time I would re-evaluate my position.