Be safe!

Also drive around and look for indications on whether this area is safe, clean, or on the way up or down in terms of condition and crime.Pull the Neighborhood Crime Information: Most metropolitan police departments either have web sites or information they can give on a particular area.

Also, I see it has MDE certs...but is that for lead free or lead safe?

I think it's safe to say you're not underestimating its value. 

So maybe I should focus more on how to find an arrangement that give my friend the cash he needs to do repairs/downpayment on this new house, but buy myself 3-4 months (6 to be safe) to sell it after repair.And I would like to show them the profit we expect to make after all the calculations to be extra sure that they're going into this with eyes wide open -- great advice all around!

Since I am going to be deeply invested in this work financially and emotionally, I want to play safe and avoid big surprises.Thanks in advance for your feedback and guidance!

If so, doesn't that support the claim that rentals are relatively safe in a recession (if you've taken the right precautions)?

You are safe to wholesale unless you get caught than it can be very painful. 

Another point, your sister can assign her interests and your x-brother in law arising from a divorce, being family you can avoid the due on sale issues, to do that Sub-To safely  you need to see your attorney.

Him : But I don't do business like that...You: I'm sure you don't sir but you agree a contract would absolutely keep everyone safe if it did happen correct?