You simply create an LLC and split ownership pro rata. 

so currently,GP- 5% equity - 30% profitsLP - 95% equity - 70% profitsproposedGP - 5% equity - 30% profitsGP - 35% equity (raised through additional investors by GP) - 26% profit (if that previous 70% is split pro-rata)LP - 60% equity - 44% profit (if that previous 70% is split pro-rata)

For your investment, you will earn quarterly or monthly distributions, as well as your pro rata share on any capital event.

If there was a trust involved, it could have a non-pro-rata distribution clause that allows some siblings to receive different assets, so long as everyone receives an equal FMV of assets. 

I feel it might be better instead of borrowing the money from them to let them partner up and share in profits pro rata while we also take a "management fee %" off the top of the profits.

If the land contract fails and she takes the house back, then I expect that a pro-rata of the loss would be picked back up as income.Any insight would be appreciated from anyone who has encountered this situation.

You are certainly entitled to keep the pro rata portion between them leaving and you re renting the place as well as administrative costs, cleaning, etc.

Once the borrower provides proof of insurance, then OSC will refund us the cost of the policy paid, pro rata to the date of new insurance by the borrower.

Being as longer term loans generally fetch higher interest rates, not only would they cost more interest over the life of the loan, but also a higher pro rata cost on the current principal.

In this case, your investors would each own a pro-rata share of an LLC that you run.