My two sons contributed to the investment.

That's $1,516.2Each investing member will agree to be bought out after 3-5 years at their initial capital contribution plus 4% compound interest annual return.

(Side note: we also contribute the annual max to a 529 for my daughter's college tuition.

In any case I don't see myself having the time or adequate knowledge to do my own property management so I would hire a property manager, if that has a contributing factor in the advice. 

So here is a small contribution of mine: https://www.mymoneyblog.com/experian-boost-review-free.htmlThis seems legit and the review is honest.

Thanks all for your contributions.

Also keep in mind an A where I invest may be a B where you do.The main contributing factors to determine grades are: location, features/amenities, condition, and age of property.  

It will generate $400 month of cash flow once we move out and our total cash contributed to the property to date is $14,000.

I'm a developer - buy, entitle, permit, finance, build, operate larger projects - but regularly have to deal with the same thing you're asking about - how can I fairly compensate someone for their contribution to a project? 

You could use the listing agent for both sides and try to negotiate something....maybe a 1-2% reduction in commission which could be a reduced price by that much of a seller contribution to your closing costs.