Of all the nonsense I have heard about real estate investing, using the notion of "protecting assets" as a reason for leverage is one of the dumbest. 

I'm excited to learn and grow and eventually contribute to the vast knowledge here. 

He wants to give the house to the 4 children and 2 of the children are willing to contribute added capital to improve the house so that Dad can live there for the rest of his life, he is currently 80 years old.  

He would be mostly learning and not contributing a whole lot besides some onsite coordination, surpervising and probably some input on design and materials.

It doesn't look like you would be getting much from the sec121 exclusion.Not sure how selling this property would get your more funds into your Roth IRA, unless it just because it frees up money to make the contribution..If you need funds to build up a reserve / rain day fund / etc., this might be a way to go... 

Hard or private money would both suit your needs, depending on how many funds you have to contribute.

😁Thank you in advance for your contributions.

Assemble a team of individuals who can split following responsibilities: contribute the earnest deposit money, guarantee the loan, find the deal/conduct the diligence, raise the capital and manage the building.

What documents would you require before you contributed funds in any amount?

I only contributed financially and gave some design ideas.