Being listed on multiple OTA allows users that use alternate OTAs to see your STR and could provide a higher ADR even if you end up lower ranked of the OTAs.Basically it comes down to having all your eggs in a single basket and is too risky for my liking.i am one of those STR owners that corrects anyone that refers to my STR or STR business as an AirBnB.  

Risk that you will short yourself by not maximizing your cost seg potentialThat said, when full-service cost seg is not economically sensible, DIY is a valid alternative

Or alternatively any of the following that would have a similar outcome.

Was the 'average' alternative investment in 2021 with 200k unoquivocally better than holding the asset (and by 50-100k)? 

There is a much better alternative!

.: I'm looking into alternative ways to sell a rundown house for my parents.

Best case under such circumstance is they find alternative financing and simply over paid for the property.good luck

. $40k will not get you a non owner occupied San Diego property unless you find some unlikely alternate financing.

Are there alternative strategies you’d recommend for this market or nearby markets which are of commuting distance to Danbury?

Alternatively, you could split it between House 2 and 3 in a way that covers your building budget for the apartment.