At one of the sites the guy and the previous owner were married so he managed the property.

Once that's set, it's really not a super difficult thing to run--the biggest deal for most people is needing to be married to your phone in a way that other RE investments don't require, because you always have to be able to answer inquiries and accept bookings, and if you're not fast enough, people will often move on to other listings.You can definitely self-manage properties remotely, but it is necessary to have some kind of boots-on-the-ground help, whether for maintenance or even just helping guests with occasional issues that pop up (confusion about TV cable box remotes, etc.).

REI areas of interest (what I like learning about and may take action on):Small Multi-Family AND converting SFH to multi-familyFix and FlipBuy and Hold long term or mid-term rentalsBRRRLand Flipping and Land EntitlementsModular/Mobile/Tiny homesForeclosures and Tax LiensAbout Me: 40 yrs old, married, working mother of 2.

My personal take away is that you might as well marry the guy.! 

The father is married and has another child, and a few years ago he mentioned that he and his wife's mortgage is covered by an AirBnB rental guesthouse in their backyard. 

Have they been married and filing separately? 

Perhaps if you happen to be married, consider options for your partner to become REP. 

I had a girlfriend, but wasn't married.  

(Single - over $518,900 Married - over $583,750)One thing to note is that the tax wouldn't be due until you file taxes for 2024 and there are plenty of ways to offset that taxable gain. 

Yes if it is primary and you lived there for 5 years, probably do not need 1031 as up to 500k is tax free for married filing jointly and 250k for individuals.