A HELOC is certainly an option if you could pay it off rather quickly or else you'll end up paying a whole lot in interest layer one. 

It may sound nice to pay a 6% management fee but the extra fees can add up to be more than the other company that charges 10% with no additional fees.

The contractor will give you better pricing the more you use them, some GCs increase their price, but those are the ones you would like to not use (side note, of course with inflation you need to pay your people right, but it needs to be reasonable).

I know what seller financing would involve in regards to me (the buyer) having to pay a interest rate set by the seller and the monthly payments also set by seller.But what are the benefits of seller financing a property?

Now a "Foriegn National Mortgage" has similarities to those mortgage types but you will pay a higher interest rate and be required to have a higher downpayment as well (usually about 35% down). 

Will they continue paying market rent for a mismanaged property. 

The allowable rent increase is not typically the big issue with rent control, the bigger issue is getting rid of poor tenants that pay their rent.

Working with the family to pay the lease.  

I just read an article recently that noted "Avg Profits For Flipped Homes" of $80,000, however when you dig into the article and their sources, "Profit" is simply Sale Price - Purchase Price...so it doesn't consider renovation costs, holding costs, financing costs, etc.

Every month, property 2 has been paying most of the mortgage on that Property 1 home equity loan.