All depending on perspective.I would take it with a big grain of salt, I think Opendoor is trying to drum up interest, given how many properties, they and other institutional buyers, are having on the market (e.g.

Valuation depends on your market = i.e. volume of STR supply and regulations. 

Depends on their health and any desire they may have to simplify.

$100 a month is not enough for a duplex depending on age.how well do you know this market?  

Best I can tell all in all we about 3X cash on cash over 5 years.infil lots depending on lot we could double our money in 9 to 12 months cash on cash.. so on and so forth.

Learnt lesson not to fully depend on property manager and should have made decision faster by reducing rent .

I would anticipate it would depend on the level of detail you desired but it has been my experience that the will do free estimates.

Suggesting to them buying their house for a wholesale range offer or lower dependent on the extent of the rehab, then having a contract in place that gives them a percentage of the profit to help get them back on their feet, paying off debts etc.

Will depend on several factors like the type of property, type of tenants, your risk tolerance, other assets you own, your estate planning, laws where the property is located, etc.

As a few mentioned, depending on your situation you might have to do a DSCR Cashout (vice conventional investment), and with hard money loans often there is a pre-payment penalty.