The loan is not recourse to the retirement plan member.Work with a tax professional who knows what they're doing to ensure the 401k member isn't incurring UBTI via UDFI.

So with the house hacking and favorable financing option via FHA, is there any terms that come with owning a duplex etc. where you have to reside in it for a certain amount of time?

It's those maniacs that buy homes cash via quit claim deed off of craigslist that really get screwed.Make sure your property manager is a licensed real estate brokerage.Google Clayton Morris and/or Morris Invest for a cautionary tale of what not to do when buying turnkey real estateUnderstand you can not eliminate all risk, only mitigate it.

I even have them show me properties via facetime.

I personally run my spreadsheet via photos.

It's those maniacs that buy homes cash via quit claim deed off of craigslist that really get screwed.Make sure your property manager is a licensed real estate brokerage.Google Clayton Morris and/or Morris Invest for a cautionary tale of what not to do when buying turnkey real estateUnderstand you can not eliminate all risk, only mitigate it.

My wife and I bought our first house in May 2019 via 25yr Mortgage.

Here're some articles to help you further. https://www.biggerpockets.com/member-blogs/10850/85836-should-i-buy-a-turn-key-property-or-invest-in-a-syndicationhttps://www.biggerpockets.com/member-blogs/10850/84064-what-type-of-investor-to-be-when-i-grow-up-active-or-passivhttps://www.biggerpockets.com/member-blogs/10850/86626-the-pros-and-cons-of-investing-via-real-estate-syndication

Then look up reviews about the lender (via google/biggerpockets). 

If you are reasonably certain that the son has inherited the property, and you are content to rent the property for cash flow, then go ahead and offer the son $10k for signing his interest over to you via a "Quit Claim Deed'.